Adaptable personalized thermoregulation through rational design of passive and active heat transfer

Adaptable personalized thermoregulation through rational design of passive and active heat transfer | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Adaptable personalized thermoregulation through rational design of passive and active heat transfer Jinwoo Lee, Seung Hwan Ko, Yeongju Jung, Dong Hyun Kim, Farooq Khan, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8884215/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted You are reading this latest preprint version Abstract As extreme weather events become increasingly frequent and severe, sustaining thermal homeostasis under variable environmental conditions has become a growing challenge for maintaining thermal comfort and physiological stability. This study presents an energy-efficient, personalized thermoregulatory wearable that rationally integrates multimodal active and passive heat transfers to maintain human thermal comfort in all-weather conditions. The device offers a reversible operation in four distinctive modes: passive heat transfer through (i) radiative and evaporative cooling and (ii) solar heating, and active heat modulation through (iii) thermoelectric cooling and (iv) heating. The device employs an invertible, dual-sided architecture that enables switching between cooling and heating modes. Under mild weather conditions, the wearable maintains skin temperature within the thermal comfort zone through purely passive operation without external energy input. Under extreme conditions, it synergistically combines passive and active thermoregulation to sustain thermal comfort across ambient temperatures from − 10°C to 50°C. Compared with a conventional thermoelectric device, the proposed design reduces energy consumption by 14.3% and 24.9% for cooling and heating, respectively, during a 600-s operation. By adaptively offering both passive and active thermoregulatory modes, this work provides an energy-efficient strategy for personalized thermal management and effective thermal homeostasis in all-weather environments. Physical sciences/Engineering/Mechanical engineering Physical sciences/Energy science and technology/Thermoelectric devices and materials Figures Figure 1 Figure 2 Figure 3 Figure 4 Introduction As global climate change accelerates, extreme weather events, such as prolonged heat waves and cold spells, pose serious threats to human health and well-being. In this regard, effective thermoregulation not only preserves thermal comfort but also addresses a critical issue in public healthcare. Prolonged exposure to elevated or depressed temperature is directly associated with increased risks of heatstroke, hypothermia, cardiovascular strain, and even mortality, particularly among thermally vulnerable populations such as the elderly or outdoor workers 1 . For instance, in 2025, the exceptional heatwave in Spain recorded 1,180 heat-related deaths, which was more than ten times higher than in the same period in 2024, highlighting the severe mortality risks posed by recent extreme climate events 2 , 3 . Despite growing attention to personal thermal regulation, previous thermal management technologies remain limited in their energy-efficiency. Active thermal devices, such as thermoelectric (TE) modules, offer promising solutions for wearable active thermal regulation strategies, owing to their ability to provide both cooling and heating within a single architecture. Recent advances in materials science and engineering have enabled the implementation of TE devices in human-centric wearable designs, improving stretchability and wearing comfort for continuous use 4 , 5 . Nevertheless, TE-based systems rely exclusively on externally supplied electrical power to induce thermal modulation, which fundamentally constrains their energy efficiency and poses a significant challenge for sustainable wearable applications 5 . In this regard, passive heat-transfer strategies, including radiative cooling (RC), evaporative cooling (EC), and solar heating (SH), have attracted considerable interest as zero-energy approaches to personal thermal management 6 – 8 . However, these methods typically operate in a single thermal mode and strongly depend on ambient environmental conditions. As a result, their limited heat-transfer capacity produces insufficient power to regulate body temperature, as they rely on passive mechanisms, particularly under extreme weather conditions. In summary, both active and passive thermal devices fall short of offering a viable solution for supporting thermal homeostasis in real-world scenarios. Therefore, a rational integration of passive and active thermoregulatory strategies is essential to achieve energy-efficient, adaptable thermal regulations. Despite this need, to the best of the authors’ knowledge, no prior study has demonstrated thermoregulatory wearables that seamlessly integrate (i) radiative and evaporative cooling, (ii) photothermal solar heating, (iii) active thermoelectric cooling, and (iv) heating within a single reconfigurable platform. Although TE systems incorporating RC or SH have been reported, these efforts have predominantly focused on energy harvesting or power generation 9 – 11 . As such, their design principles, performance metrics, and operational objectives are fundamentally different from those required for human-centered thermoregulation. Here, we present an energy-efficient, personalized thermoregulatory wearable that rationally integrates passive and active heat transfer modes within a single platform, delivering adaptive temperature control in all-weather conditions. Unlike existing devices that rely exclusively on either active or passive heat-transfer mechanisms, this study combines both into an all-in-one system with distinct cooling and heating modes. The device enables passive thermal regulation under mild conditions and switches to an integrated mode that synergistically couples passive and active thermoelectric control under extreme environments, while reversible operation allows bidirectional temperature modulation. The device comprises two opposing functional layers, which are integrated across a TE module: a hexagonal boron nitride (h-BN)-elastomer composite layer for RC 12,13 , and an electrospun graphene-thermoplastic polyurethane (TPU) nanofiber membrane for broadband solar absorption and directional sweat evaporation 14 – 16 . Notably, EC is incorporated into the SH layer, as this layer interfaces directly with the skin during cooling operation. To facilitate efficient EC in the SH layer, we engineered a wettability gradient across the membrane thickness to enable capillary-driven moisture uptake at the skin interface 17 – 19 . Lastly, for bidirectional thermoelectric temperature modulation, we employed the passive layers as substrates and soldered an array of Bi 2 Te 3 thermoelectric legs on top of interconnecting serpentine Cu electrodes 20 , 21 . As a result, during active TE modulation, passive heat transfer takes place alongside the active mode, enhancing thermoregulation and reducing energy consumption. Especially, through combined theoretical simulations and experimental validation, we demonstrate an energy-efficient thermoregulation strategy across diverse climatic conditions. In this regard, by integrating passive and active thermoregulation with bidirectional functionality in a single device for the first time, this work advances future wearable thermal technologies that can sustain human comfort in extreme climates while reducing energy demand. Results & discussion 2.1 Overview of the device architecture and its operating mechanism Figure 1 a provides a graphical illustration of the structural design, which is rationally engineered to adaptively regulate skin temperature through invertible orientation for reversible cooling and heating. The overall device comprises RC and SH-EC layers, which are positioned on opposite sides of vertically stacked thermoelectric legs. The TE layer consists of a \(\:10\times\:10\) array of vertically aligned Bi 2 Te 3 legs, which are soldered to laser-patterned serpentine copper electrodes. In the heating mode (H-mode), the SH layer faces up and absorbs incident solar radiation, which is transferred through the TE module to warm the skin-contact side. Conversely, in the cooling mode (C-mode), the RC layer is oriented upward to reflect incident sunlight, while enabling thermal radiation to the sky and heat extraction from the body through the TE legs. Simultaneously, the SH-EC layer in contact with the skin wicks sweat away from the skin toward the exterior, generating a synergistic EC effect. Notably, although EC might intuitively be incorporated into the RC layer, it is instead deliberately integrated into the SH layer. This design choice is based on the device configuration in cooling mode, in which the SH layer is in direct contact with the skin and therefore directly governs moisture exchange with the body. Accordingly, hydrophobic and hydrophilic bilayers constitute the SH-EC layer to facilitate unidirectional fluid transport, ensuring effective EC when the RC layer faces the sky. Based on this rationally designed architecture, the user can switch between operating modes simply by flipping the device. When passive SH or RC/EC alone is insufficient, the TE module provides active heating or cooling to maintain the target temperature. Figure 1 b shows the corresponding top and side views of the device for each mode. To elaborate on each heat transfer mode in detail, Fig. 1 c delineates four distinctive modes: (i) integrated heating mode, (ii) eco-heating mode, (iii) eco-cooling mode, and (iv) integrated cooling mode. The integrated heating mode synergistically combines SH and TE heating, delivering intense heating to regulate body temperature in extremely cold weather (Mode 1). On the other hand, the eco-heating mode utilizes SH to provide moderate thermal output without electrical power consumption, making it suitable for mildly cold conditions (Mode 2). Similarly, the eco-cooling mode relies on RC and EC to produce mild cooling without external energy input (Mode 3), whereas the integrated cooling mode enhances the cooling performance by incorporating TE cooling, enabling effective thermoregulation under extreme heat conditions (Mode 4). Figure 1 d illustrates a schematic summary of the operational modes and the associated heat-transfer mechanisms under solar irradiation. From an energy consumption perspective, as shown in Fig. 1 e, SH, RC, and EC operate through passive heat transfer mechanisms that require no electrical input, thereby obviating the additional amount of energy needed to achieve thermal comfort under mildly chilly or warm environmental conditions. Besides, even under extremely cold or hot conditions, the incorporation of these passive heat transfer mechanisms substantially reduces the overall energy required to reach the thermal comfort zone when compared with conventional thermoelectric devices that rely solely on active heat transfer. Consequently, the rational integration of passive and active heat transfer mechanisms enhances energy efficiency while maintaining effective thermal regulation across a wide range of environmental conditions, surpassing the limitations of conventional thermal management strategies. The detailed validation based on theoretical calculations is discussed in the following section. 2.2 Optical properties of SH-EC and RC layers Figure 2 a shows actual photographs of the SH-EC and RC layers, along with scanning electron microscopy (SEM) images of their microstructures in the inset figure. Since we electrospun the SH-EC film, it consists of a nanofiber network with varying pore sizes, whereas the RC layer shows a flat, non-porous microsurface, as it was made by mold-casting. Supplementary Fig. 1 presents cross-sectional SEM images of the SH-EC layer, which clearly show a bilayer structure consisting of hydrophilic and hydrophobic layers. To evaluate the optical properties of each layer, we conducted spectroscopic characterization on the RC and SH-EC films using ultraviolet-visible-near-infrared (UV-Vis-NIR) and Fourier transform infrared (FTIR) spectroscopy, as presented in Fig. 2 b. The SH-EC layer exhibits a low broadband reflectance of 13.4% over 300–2500 nm, indicating strong solar absorption (86.6% absorption) by the embedded graphene nanoplatelets (GNPs). The near-zero bandgap of graphene enables broadband interband absorption across the solar spectrum. Meanwhile, the nanoplatelet morphology increases the effective optical path length through multiple light-scattering events, which serve to further suppress reflectance. 15,22 Also, we selected TPU as the electrospinning matrix due to its high solution processability, elasticity, and ability to form mechanically robust fibrous networks with tunable wettability 23 , 24 . In contrast, the RC layer consisted of a h-BN/Ecoflex composite, designed for high solar reflectivity and mid-infrared emissivity. h-BN possesses a wide bandgap (≈ 5.9 eV) and strong phonon-polariton resonances in the 8–13 µm atmospheric window, making it ideally suited for RC applications 25 . When randomly dispersed within the Ecoflex matrix, h-BN nanoplatelets induce strong multiple-scattering effects, further enhancing broadband solar reflection. Furthermore, we deliberately employed nanoplatelet-shaped h-BN to maximize RC performance by promoting anisotropic scattering and increased optical path lengths 26 . Spectral analysis showed reflectance of 95.8% across the solar spectrum, and the FTIR results confirmed a mid-IR emissivity of 92.3%. We calculated the emissivity based on Kirchhoff’s law, which stipulates that for opaque bodies in thermal equilibrium, the spectral emissivity equals spectral absorptivity ( \(\:\epsilon\:=1-\text{R}\) ) 27 . These optical characteristics enable the RC film to reflect incoming solar radiation while efficiently dissipating internal heat to the sky, promoting RC. Based on the optical results of SH-EC and RC layers, we theoretically calculated the cooling and heating power of each layer with rising convective heat-transfer coefficient ( h ) in the range from 0 to 8 W·m − 2 ·K − 1 with an increment of 2 W·m − 2 ·K − 1 at the ambient temperature of 300 K. The result shows that the cooling and heating power of RC and SH-EC films corresponds to 81.7 W·m − 2 and 732.8 W·m − 2 , respectively (Fig. 2 c ) . The detailed data for calculations is presented in Supplementary Fig. 2 . To validate passive performance under real-life conditions, we performed an outdoor field test (September 26th, 2025, in Seoul, South Korea) using the experimental setup as in Fig. 2 d. To isolate the samples from environmental thermal effects, we placed the RC and SH-EC samples on an insulation box to minimize conduction and added an aluminum foil lining to reduce heat transfer from exterior radiation. We also recorded the sample and ambient temperature with separate thermocouples housed inside the windshield to diminish the effect of air convection (Fig. 2 e). Relative to the ambient temperature, the RC film remained sub-ambient for most of the experimental period, with average and maximum temperature differences of 2.55°C and 8.0°C, respectively. By contrast, the SH film exhibited strong solar-driven heating with mean temperature difference of 11.45°C, achieving a maximum super-ambient rise of 24.6°C. Notably, although earlier studies primarily relied on wind-shielded conditions 28 , recent investigations have increasingly considered airflow to better approximate real-world environments 29 . Consistent with this approach and considering the intended practical use of the fully assembled device on human skin, we conducted outdoor experiments under airflow-exposed conditions ( Supplementary Fig. 3 ), offering the thermal management performance comparable to those reported in recent airflow-considered studies 29 . Overall, these results corroborate the spectroscopic trends of the SH-EC and RC layers and confirm thermal functions under realistic outdoor conditions. 2.3 Evaporative cooling performance and sweat managing function of the SH-EC film Apart from RC and TE cooling, we incorporated EC mode into the system by engineering the wettability across the membrane thickness. To attribute evaporative functionality to a wettability gradient, we employed electrospinning to deposit hydrophobic and hydrophilic layers on top of one another. The hydrophobic side of the membrane features loosely packed and coarse fibers, whereas the hydrophilic side exhibits finer fibers in a much denser network to promote unidirectional liquid transport from hydrophobic to hydrophilic sides 30 , 31 . By controlling the pore size and surface chemistry of the electrospun membrane, the Laplace pressure can be engineered to drive liquid flow in one direction, as shown in the equation below: $$\:\varDelta\:P=\frac{2\gamma\:cos\theta\:}{r}$$ where \(\:\gamma\:\) , \(\:\theta\:\) , and \(\:r\) correspond to surface tension, contact angle, and radius of the pore. Based on the equation, on the hydrophobic face, larger pores should minimize the initial barrier to fluid flow through, while smaller pores amplify capillary suction on the hydrophilic side. This creates a steep Laplace pressure drop across the membrane thickness, driving spontaneous unidirectional transport. To realize the effective liquid transport across the membrane, we first tailored the pore size on each side of the membrane. Figure 2 f shows the pore size of hydrophobic and hydrophilic layers along with the snapshots of their water contact angle in the inset figure. After optimizing the electrospinning conditions to control the membrane pore structure, we obtained average pore diameters of 0.515 µm and 0.101 µm on the hydrophobic and hydrophilic sides of the membrane, respectively. In addition, Supplementary Fig. 4 shows SEM images of the hydrophobic and hydrophilic sides, which clearly exhibit distinct pore sizes and fiber architectures that contribute to the contrasting wettability of the layers. To further enhance the hydrophilicity, we incorporated an amphiphilic triblock copolymer (Pluronic F127) into the nanofiber matrix, as Pluronic F127 consists of functional PEO and PPO groups within its chains. Therefore, the PEO blocks form hydrogen bonds with water molecules while the PPO blocks anchor into the TPU fiber matrix, effectively converting the originally hydrophobic surface into a hydrophilic one. Supplementary Fig. 5 presents EDS images of the hydrophobic and hydrophilic layers, in which the hydrophilic side exhibits a higher oxygen-to-nitrogen (O/N) atomic ratio than the hydrophobic side due to the high oxygen content of F127. EDS analysis revealed O/N ratios of 3.02 and 2.09 for the hydrophilic and hydrophobic layers, respectively ( Supplementary Fig. 6 ). Using the collective effect of combining pore-size optimization with an amphiphilic triblock copolymer, we were able to engineer a pronounced wettability gradient across the membrane thickness. Water contact angle measurements confirmed this asymmetry: the hydrophobic surface exhibited a contact angle of 114.3°, while the hydrophilic surface showed a near-zero contact angle (≈ 0°). Figure 2 g explains the unidirectional fluid transport mechanism by using the wettability gradient across the membrane thickness. As the figure depicts, the water droplet can penetrate the bilayer membrane only at the hydrophobic surface because the smaller pores on this side generate a high threshold pressure that must be exceeded to initiate penetration. Once the droplet enters the membrane and reaches the hydrophilic region, the larger pores and strong capillary suction lower the hydraulic resistance and drive the liquid forward, preventing reverse flow from the hydrophilic to the hydrophobic side. On the other hand, if the water droplet enters the membrane from the hydrophilic side, the liquid initially wicks into the porous network due to strong capillary suction. However, once it approaches the hydrophobic region with smaller pores, the high breakthrough pressure prevents further penetration, causing the liquid to spread laterally on the adjacent hydrophilic region. To characterize the fluid transport mechanism, we conducted two complementary tests, as shown in Fig. 2 h and Supplementary Movie 1 . The top sequence of images illustrates cross-plane capillary pumping: a dyed water droplet placed on the hydrophobic surface penetrates the membrane and is transported to the hydrophilic side within 9 s. In contrast, when the droplet is applied to the hydrophilic surface, only a negligible amount of liquid passes through the membrane, leading to spreading into the neighboring hydrophilic region. This asymmetric behavior follows Laplace pressure-driven transport, in which the wettability gradient determines the direction of liquid flow. 32,33 . Correspondingly, Supplementary Fig. 7 and Supplementary Movie 2 demonstrate the anti-gravity direction of fluid transport, in which the fluorescently dyed water is transported from the hydrophobic to the hydrophilic side against gravity due to capillary pumping. Yet, when water was applied to the hydrophilic side, the droplet spread laterally into the adjacent hydrophilic regions, corroborating unidirectional anti-gravity fluid transport. Along with evaporative cooling capability, the unidirectional fluid transporting function of the SH-EC layer facilitates sweat management during the C-mode, potentially enhancing the wear comfort. The moisture management tester (MMT) analysis in Fig. 2 i further validates this directional transport behavior 34 . The membrane exhibits a directional transport index (R) of 626%, which exceeds conventional moisture-wicking performance and indicates strong capillary pumping combined with effective barrier-layer functionality 35 . To evaluate the evaporative cooling performance of the SH-EC layer, we conducted comparative drying experiments using commercially available textiles, including regular cotton and a moisture-wicking sports fabric (Nike Dri-FIT) 36 . EC occurs as water molecules (or sweat) absorb latent heat from the SH-EC surface and undergo a phase change from liquid to vapor, thereby removing heat from the surface without increasing the temperature of the remaining liquid ( Supplementary Fig. 8 ). Figure 2 j presents the temporal mass-loss profiles measured while each sample was placed on an artificial skin substrate maintained at 35°C via PID (Proportional-Integral-Derivative) temperature feedback control. In each test, 100 µL (0.1 g) of water at 66°C was dispensed onto the fabric surface, and the residual mass, 𝑚(𝑡), was recorded under identical ambient conditions (22.0 ± 0.5°C). The SH-EC layer reached complete drying (𝑚 = 0) within 8 minutes, whereas cotton and Dri-FIT required 30 and 31 minutes, respectively. These results indicate that the SH-EC layer enables markedly faster evaporation, primarily due to its rapid liquid-transport capability. Additionally, to verify the practical cooling effect of evaporative cooling, Fig. 2 k and 2 l compare evaporation rates and average skin temperatures with those of commercial fabrics. Using the identical experimental setup as previously, the evaporation event was identified by the characteristic cooling plateau followed by a rapid temperature rise, marking the transition to the dry state. From these intervals, we extracted the effective evaporation rates of 0.559 mL·h⁻¹, 0.400 mL·h⁻¹, and 0.123 mL·h⁻¹ for the SH-EC layer, cotton, and Dri-FIT, respectively (ambient 22.0 ± 0.5°C). Similarly, the corresponding average skin temperatures during the evaporation period were 29.7°C, 30.1°C, and 28.9°C, respectively. In addition, we compared the cooling performance of each material in detail, as summarized in Supplementary Fig. 9 . Thus, these sequential results confirm that the SH-EC layer achieves the highest evaporation rate and cooling effect among the tested materials, demonstrating efficient capillary-driven liquid uptake and vapor transport. 2.4 Active thermoelectric cooling/heating characterization To enable reversible, electrically driven thermal modulation, the device incorporates a π-type TE module, which is positioned between the RC and SH-EC layers. As thermoelectric leg materials, Bi 2 Te 3 was selected for its high thermoelectric figure of merit (zT ≈ 1 near 300 K) and superior carrier mobility at skin-relevant temperatures, making it one of the most efficient inorganic TE materials for wearable applications 20 , 37 . Each pellet, 2.5 mm in height, was soldered onto laser-cut serpentine copper interconnects using eutectic solder paste. This alloy provides low-melting-point processing (~ 183°C) and excellent wetting behavior, while forming intermetallic compounds such as Cu 6 Sn 5 and Cu 3 Sn at the Cu-solder interface 38 , 39 , which enhance thermal stability and electrical bonding strength. The serpentine Cu electrode accommodates mechanical deformation through in-plane stretching and buckling, maintaining stable electrical connectivity during flexing and bending 40 . Figure 3 a presents the assembled device, showing the SH-EC and RC layers oriented upward when the device is bent or stretched. In addition to providing RC, EC, and SH functionalities, we incorporated highly thermally conductive fillers into the elastomer to enhance thermal conductivity, consequently improving the efficiency of active heating and cooling in the module. We incorporated h-BN nanoparticles into Ecoflex for the RC layer and GNPs into TPU for the SH-EC layer. In addition to enabling the desired optical functionalities, the incorporation of these particles simultaneously enhances the thermal conductivity of each layer. Notably, most previous RC studies have relied on porous structures to achieve favorable optical properties. While such designs are effective in enhancing solar reflectance and mid-infrared emissivity, they generally suffer from low thermal conductivity, which limits their suitability for wearable applications that require efficient heat transfer. To address this limitation, we incorporated h-BN nanoparticles into the Ecoflex matrix, increasing the thermal conductivity to 0.471 W·m − 1 ·K − 1 , representing a 2.69-fold increase over the pristine elastomer (Fig. 3 b). Similarly, for the SH-EC layer, a porous structure is inherently required to enable sweat evaporation, which would compromise thermal conductivity. To overcome this intrinsic trade-off, we introduced GNPs into the TPU matrix, boosting the thermal conductivity to 0.610 W·m − 1 ·K − 1 , representing a 2.10-fold increase relative to bare TPU. This strategy effectively addresses the thermal properties associated with porosity while preserving evaporative cooling functionality (Fig. 3 c). To validate the effect of thermal conductivity on heat transfer between the device and the human skin, we performed a Multiphysics numerical simulation for cases with and without thermally conductive fillers (Fig. 3 d and 3 e). Thus, we computed the transient temperature response of the finger-tip interface with the device over a 300 s time window. It should be noted that heating and cooling were evaluated on both sides of the device, reflecting its intended wearable operation. Specifically, when heating the skin, the h-BN/Ecoflex RC layer is in contact with the skin, whereas for cooling, the SH-EC layer interfaces with the skin. Accordingly, for the h-BN/Ecoflex RC layer, TE heating was applied to evaluate heat transfer from the RC layer to the fingertip. At a device temperature of 50°C, the sample incorporating h-BN fillers exhibited a mean interface temperature that was 1.12°C higher than that of the pristine sample, corroborating enhanced heat-transfer efficiency. Conversely, for the SH-EC layer, TE cooling was employed to assess cooling performance at the skin interface. At a device temperature of 15°C, the sample achieved an average temperature reduction of 0.25°C, compared with the neat sample, demonstrating improved cooling effectiveness. Although these simulations assume idealized, complete thermal contact at the skin-device interface, the results clearly indicate that loading with thermally conductive fillers enhances heat transfer between the device and the skin. Such enhanced thermal transport can potentially reduce the electrical energy required to operate the TE module, because it can achieve the same level of heating or cooling with a lower electrical input. To demonstrate temperature controllability, we varied the applied voltage, as it directly modulates the TE cooling and heating output. For instance, Fig. 3 f depicts the time-dependent temperature response of the heating mode as the electrical input ranges from 1.0 V to 1.5 V in increments of 0.1 V, resulting in a temperature rise of 21.7°C at 1.5 V. The IR images in Supplementary Fig. 10a illustrate the residual heating effect on the human hand after the TE device is removed. Similarly, Fig. 3 g presents the TE cooling response, in which the applied voltage is varied from − 1.0 V to -2.0 V in 0.2 V, yielding temperature drops of up to 13.6°C. As in heating mode, cooling mode also leaves a residual cooling effect on the skin ( Supplementary Fig. 10b ). These results confirm that both TE heating and cooling modes are capable of providing effective heat transfer at the skin surface, enabling sufficient control of body temperature. Since wearable devices must withstand mechanical stresses associated with everyday use, we performed a series of mechanical durability tests to evaluate the fatigue strength of the device. Supplementary Fig. 11a demonstrates the effect of varying bending radius on the normalized electrical resistance of the device over a range from the flat state to 4.5 mm. The results show negligible variation in normalized resistance with decreasing bending radius, indicating excellent mechanical robustness even under severe curvature. Additionally, as mechanical failure in practical applications typically originates from fatigue caused by repeated deformation, we further assessed the device's durability by monitoring the normalized resistance during cyclic bending with a bending radius of 3.5 mm. As shown in Supplementary Fig. 11b , the normalized resistance remains nearly constant over 1000 bending cycles, confirming stable electrical performance under repeated mechanical loading. In addition to bending tests, tensile deformation experiments were performed to evaluate the device’s tolerance to stretching. Figure 3 h shows the normalized resistance as a function of tensile strain, increased incrementally by 10% up to a maximum strain of 140%. The resistance remains stable throughout the entire strain range, demonstrating reliable electromechanical stability even under large deformation. To further examine fatigue resistance under tensile loading, cyclic stretching tests were conducted at 30% tensile strain (Fig. 3 i). Although minor fluctuations in resistance are observed during cycling, no mechanical failure or performance degradation occurs over 1000 stretching cycles, substantiating the mechanical robustness of the device under repeated mechanical loading associated with everyday wear. Furthermore, to verify the stable TE operation under mechanical deformation, we applied tensile strain of 30% to the device during active TE operation (Fig. 3 j and 3 h). When compared with the pristine device under no mechanical loading, the strained device exhibits comparable heat-transfer performance in both cooling and heating modes, corroborating that mechanical deformation does not significantly degrade TE functionality. 2.5 Energy efficiency and heat transfer evaluation of fully assembled thermoregulatory wearable To demonstrate energy-efficient thermoregulatory operation, we numerically calculated the power required for the device to maintain skin temperature within the thermal comfort zone under arbitrary weather conditions and compared it with that of a conventional thermoelectric device (cTED) over 60 s. The temperature profiles in the top row of Fig. 4 a show the time-dependent skin-device interface temperature when the device maintains skin temperature within the thermal comfort zone, along with the corresponding ambient temperatures under extreme and variable weather conditions. The bottom plots display the calculated power consumption required to achieve the observed thermoregulatory performance. In parallel, Fig. 4 b presents the corresponding results obtained under identical weather conditions using cTED that relies solely on active TE heating and cooling. We excluded the effect of EC from numerical simulations because its cooling strength depends on the amount of water undergoing phase change, which varies with user-specific and environmental conditions and cannot be reliably prescribed in the model. Compared to the proposed device that employs passive, energy-free heat transfer under mild weather conditions, cTED requires 8.61 J and 63.1 J to reach the thermal comfort zone, respectively ( Supplementary Fig. 12 ). Moreover, even under conditions that necessitate active control, when compared to cTED, the integrated modes of the proposed device exhibit energy reductions of 2.13 J for cooling and 5.31 J for heating over a 60 s time window. This energy advantage becomes more pronounced as operation time increases. For example, as shown in Fig. 4 c, extending the operation time to 600 s yields energy savings of 6.60 J and 32.3 J for integrated cooling and heating, respectively. These savings correspond to reductions of 14.3% and 24.9% in total energy consumption enabled by the incorporation of passive heat-transfer modes. Supplementary Fig. 13 provides the simulation-based temperature evolution for four different heat-transfer modes over 60 minutes of operation under identical boundary conditions. The simulation results indicate that the active heat-transfer modes reach the temperature extremes shortly after the onset of the TE operation. After the active modes approach the temperature extremes, the temperature response begins to plateau, with the temperatures at 60 min computed to be − 2.48°C and 53.8°C for the active TE cooling and heating modes, respectively. On the other hand, the passive heat-transfer modes exhibit a more gradual temperature change over time, resulting in temperatures of 8.21°C and 51.1°C at 60 min for RC and SH, respectively. The simulation results highlight the complementary roles of passive and active heat-transfer modes, wherein passive mechanisms provide gradual and energy-free thermal regulation, while active thermoelectric operation enables rapid response to temperature extremes and precise thermal control. To analyze the practical performance of the active heating and cooling modes, we experimentally simulated thermally harsh environments of 50°C and − 10°C on average and placed an artificial skin substrate in each environment. To emulate the thermal load of human skin, we applied electrical power (4 W) to silicone substrate to maintain 35°C at room temperature. In addition, a PID feedback controller was implemented to rapidly drive and maintain the temperature within the thermal comfort zone (35°C). Supplementary Fig. 14 illustrates the PID control architecture used for closed-loop temperature regulation of the TE device. For TE cooling mode (at 50°C on average), Fig. 4 d shows that the device is capable of maintaining the temperature of the artificial skin within the thermal comfort zone (T c ). The incorporation of PID feedback control allows the device to reach T c rapidly and regulate the artificial skin temperature within this range thereafter. Conversely, the bare artificial skin without thermal regulation stabilizes at an average temperature of 53–54°C, as the applied electrical heating used to emulate metabolic heat generation adds to the imposed ambient temperature of 50°C. In contrast, Fig. 4 e shows that, in a sub-zero environment, the temperature of the bare artificial skin decreases to 1–2°C, which is a level that may induce hypothermia under prolonged exposure. On the other hand, the PID-controlled active heating mode raises the artificial skin temperature to the setpoint and subsequently maintains it within the thermal comfort zone. Figure 4 f and 4 g describe the outdoor thermoregulatory performance of the device under passive heat-transfer operation by comparing its SH and RC functionalities with bare simulated skin without the device. Again, we used artificial skin to simulate the thermal load of human skin and monitored the temperature of each sample, along with solar irradiance, over 500 s. The passive cooling mode also demonstrated effective cooling, reducing the average skin temperature by 6.76°C and the maximum skin temperature by 8.50°C. In parallel, when the SH-EC side is faced upward, the average skin temperature increased by 6.33°C, with the maximum temperature of 8.10°C, when compared with the bare simulated skin. Furthermore, to assess EC performance, Fig. 4 h compares samples with and without the EC function using the experimental setup illustrated in the inset. Throughout the experiment, we applied 100 µL of water to samples with and without EC functionalities and monitored the temperature using two thermocouples: one positioned between the device and the simulated skin (T d ), and the other attached directly to the simulated skin (T s ). The result indicates that the temperature (T s - T d ) drops rapidly when water is applied to the EC layer, whereas the sample without the EC layer does not experience a significant temperature reduction. It is estimated that 100 µL of water induces a temperature reduction of 4.3°C on average, and the EC capability effectively contributes to body temperature regulation under extremely hot conditions that induce perspiration. To examine the passive performance of the fully assembled device on actual human skin, we mounted the devices on the human forearm in two configurations, with the SH or RC side facing upward, as presented in Fig. 4 i. To monitor temperature, the thermocouple was attached to the interface between the human skin and the device, and we used PI adhesive to secure the thermocouple to the bare skin. The IR images show each sample mode on the human forearm at 100 s and 1000 s, delineating mode-dependent passive heat transfer and enhanced thermoregulatory effects over prolonged durations. The time-course of the temperature difference between each mode and bare skin is presented in Fig. 4 j, indicating that both solar heating and radiative cooling can induce a ~ 2°C change in temperature. Lastly, to showcase the practical usage of the device in real life, we integrated the devices (4 devices in a 2 \(\:\times\:\) 2 array) into the commercial garment, showing that it can be inverted to switch between heating (Fig. 4 k) and cooling mode (Fig. 4 l). Overall, the device achieves adaptive, personalized thermoregulation through a rational integration design of active TE control with passive SH, RC, and EC within a single wearable platform. By adaptively regulating skin temperature within the thermal comfort zone under extreme environmental conditions while minimizing energy consumption through passive operation, the system provides a practical route toward adaptive personal thermal management. In this regard, the proposed approach represents a significant advance over existing wearable thermal technologies by offering energy-efficient and practical personal thermoregulation in real-world settings. Conclusion This work demonstrates an adaptive thermoregulatory wearable that integrates active and passive heat transfer modes into a single device, offering personalized thermal management across all-weather conditions. Rational integration of active TE modulation with passive heat transfer not only provides adaptive thermoregulation in diverse environmental conditions but also allows efficient energy operation by prioritizing passive modes and minimizing the energy consumption of thermoelectric heat transfer. Based on the optical properties, the cooling and heating powers in the RC and SH layers show 81.7 W·m − 2 and 732.8 W·m − 2 , respectively. The outdoor test results demonstrate the notable performance of the passive heat-transfer modes: under the RC mode, the device reduces the temperature by up to 8.0°C, whereas under the SH mode, it increases the temperature by up to 24.6°C. In addition, the wettability gradient design of the SH-EC layer enables sweat removal from the skin while suppressing backflow, thereby sustaining EC and improving interfacial moisture management. EC presents an evaporation rate of 0.601 mL/h, which is more than 3.4 times that of commercial sportswear. Based on these rational designs integrating with passive heat transfer mechanisms and active TE modules, the numerical simulations demonstrated that, compared with the cTED, the integrated modes reduce energy consumption by 6.6 J and 32.3 J (comparable to the energy saving ratio of 14.3% and 24.9%) for cooling and heating, respectively, over a 600-s operation. In addition to theoretically simulated calculation, we experimentally validated that the final device maintains stable skin temperature within the comfort zone under mild to extreme environmental conditions. The PID-integrated TE heat transfer mode maintains the artificial skin temperature within the thermal comfort zone even under extreme thermal conditions of -10°C and 50°C. In contrast, under mild environmental conditions, passive thermal management alone maintains the thermal comfort zone without any energy input. Therefore, through comprehensive theoretical validation and experimental verification, the proposed system is clearly differentiated from prior wearable thermal technologies, offering a uniquely integrated, bidirectional, and energy-efficient strategy for personal thermal management. This work establishes a versatile design framework for next-generation wearable devices that is capable of maintaining thermal comfort across diverse environmental conditions while reducing energy demand and improving user comfort. Experimental section Materials Ecoflex 00–30 (Parts A and B; Smooth-On; purchased from Hyupsin Mulsan, Republic of Korea) and Slo-Jo silicone thinner (Smooth-On; purchased from Hyupsin Mulsan, Republic of Korea) were used as the elastomer matrix for the radiative-cooling composite, with hexane (Daejin Sangsa, Republic of Korea) serving as the processing solvent. Hexagonal boron nitride (h-BN; average particle size ≈ 1 µm, 98% purity; Sigma-Aldrich, Republic of Korea) was used as the radiative-cooling filler. Thermoplastic polyurethane (TPU; Shore 85A, pellet form; Sejin Poly, Republic of Korea) was employed as the polymer matrix for electrospinning. N,N-dimethylformamide (DMF, 99.0%; Daejin Sangsa, Republic of Korea) and methyl ethyl ketone (MEK, extra-pure grade; Daejin Sangsa, Republic of Korea) were used as electrospinning solvents. Graphene nanopowder (flake size ≈ 12 nm; UNINANOTECH, Republic of Korea) was used as the photothermal filler. Pluronic F127 (Sigma-Aldrich, Republic of Korea) was incorporated to impart hydrophilicity to the skin-facing electrospun layer. Copper foil (25 µm thick, annealed, uncoated, 99.8% metals basis; Thermo Fisher Scientific, Republic of Korea) was used for electrodes and electrical interconnects. p- and n-type Bi₂Te₃ thermoelectric legs (99.99% purity; Wuhan Xinrong New Materials Co., Ltd., China) were used as the active thermoelectric elements. A rosin mildly activated (RMA) solder paste (Sn63/Pb37; AON CK, Republic of Korea) was used for solder bonding. Double-sided water-soluble tape (Navimro, Republic of Korea) was employed for temporary mounting during laser cutting. Fabrication of Radiative-Cooling Layer (RC) The RC composite film was prepared via solvent-assisted mixing and mold casting. Hexane, h-BN powder, Ecoflex Part A, Ecoflex Part B, and Slo-Jo were combined at a weight ratio of 7.5:3.3:2.5:2.5:0.05 (w/w). The mixture was stirred at 30°C (700 rpm, 10 min) to homogenize the dispersion and then degassed in a vacuum chamber for 3 min. The mixture was then cast into a mold and cured at 20°C for 12 h to obtain a stretchable RC composite film. Fabrication of Solar-Heating Electrospun Layer (SH-EC) A vertically graded bilayer SH-EC membrane was fabricated by sequential electrospinning. For the hydrophobic sublayer, TPU containing graphene nanopowder (0.3 wt% relative to TPU solids) was dissolved in a mixed solvent of DMF and MEK (7:3 v/v) under stirring at 80°C until complete dissolution. The solution was electrospun onto a rotating collector at a flow rate of 0.5 mL h⁻¹ under an applied voltage of 6 kV. Subsequently, a hydrophilic sublayer was formed by adding Pluronic F127 to TPU at a 10:1 (TPU:F127, w/w) ratio and electrospinning directly on the first layer at 1.0 mL h⁻¹ under 8 kV. For both steps, the needle-to-collector distance was fixed at 10 cm. Device Interconnection and Integration After the RC layer was prepared, a copper foil was laminated onto the RC surface and patterned into the electrode layout by laser cutting. A solder mask was aligned to define the bonding pads, and solder paste was applied through the mask. Bi₂Te₃ thermoelectric legs (2.5 mm; alternating p- and n-type elements; 10 × 10 array) were placed on the paste-defined pads and soldered on a hot plate at 230°C for 20 min. For the opposite-side electrode, a copper foil was temporarily mounted on a glass slide using double-sided water-soluble tape and laser-cut into a serpentine structure. The serpentine copper electrode was then soldered to complete the electrical interconnection under the same hot-plate condition (230°C for 20 min). After soldering, the assembly was allowed to cool to room temperature before lamination. Finally, the SH-EC layer was laminated onto the opposite side of the TE core, yielding a reversible thermal skin with RC and SH-EC layers on opposing faces. The entire fabrication process of assembled device is further elaborated in Fig. S14. Characterization UV–vis–NIR spectra were acquired using a JASCO V-770 spectrophotometer over 190–2700 nm. FTIR spectra were collected using a Bruker VERTEX 70v spectrometer. Static water contact angles were measured using a KRÜSS DSA100 goniometer. Surface morphology was examined by field-emission scanning electron microscopy (FE-SEM; TESCAN CLARA LMH), and elemental analysis was performed by energy-dispersive X-ray spectroscopy (EDS) coupled to the SEM. Moisture management behavior was evaluated using a moisture management tester (SDL Atlas M290). Infrared thermography and transient temperature responses were recorded using an IR camera (FLIR A35; 45° field of view; 60 Hz). Calculation of cooling/heating power By applying the principle of energy conservation to the control volume surrounding the RC layer, the net radiative cooling power can be expressed as: $$\:{P}_{\text{n}\text{e}\text{t}}={P}_{\text{r}\text{a}\text{d}}-{P}_{\text{a}\text{t}\text{m}}-{P}_{\text{s}\text{u}\text{n}}-{P}_{\text{n}\text{o}\text{n}-\text{r}\text{a}\text{d}}$$ According to Kirchhoff’s law, the spectral emissivity is equal to the spectral absorptivity. Using the experimentally measured emissivity spectrum of the sample, each term can be evaluated as follows. The radiative power emitted from the surface is given by: $$\:{P}_{\text{r}\text{a}\text{d}}={\int\:}_{0}^{2\pi\:}{\int\:}_{0}^{\pi\:/2}{\int\:}_{0}^{\infty\:}{I}_{bb}\left(T,\lambda\:\right)\epsilon\:\left(\lambda\:\right)\text{cos}\theta\:\text{sin}\theta\:d\lambda\:d\theta\:d\varphi\:$$ The absorbed solar radiation is calculated using the AM1.5G solar spectrum as: $$\:{P}_{\text{s}\text{u}\text{n}}={\int\:}_{0}^{\infty\:}{I}_{\text{A}\text{M}1.5}\left(\lambda\:\right)\epsilon\:\left(\lambda\:\right)d\lambda\:$$ The absorbed atmospheric thermal radiation is expressed as: $$\:{P}_{\text{a}\text{t}\text{m}}={\int\:}_{0}^{2\pi\:}{\int\:}_{0}^{\pi\:/2}{\int\:}_{0}^{\infty\:}{I}_{bb}\left({T}_{\text{a}\text{t}\text{m}},\lambda\:\right)\epsilon\:\left(\lambda\:\right){\epsilon\:}_{\text{a}\text{t}\text{m}}\left(\lambda\:\right)\text{cos}\theta\:\text{sin}\theta\:d\lambda\:d\theta\:d\varphi\:$$ Non-radiative heat exchange due to convection is described by: $$\:{P}_{\text{n}\text{o}\text{n}-\text{r}\text{a}\text{d}}={h}_{c}({T}_{\text{a}\text{t}\text{m}}-T)$$ where \(\:T\) denotes the temperature of the sample and \(\:{T}_{\text{a}\text{t}\text{m}}\) represents the atmospheric temperature. The spectral radiance of a blackbody is defined as: $$\:{I}_{bb}\left(T,\lambda\:\right)=\frac{2h{c}^{2}}{{\lambda\:}^{5}\left[\text{exp}\left(\frac{hc}{\lambda\:{k}_{B}T}\right)-1\right]}$$ where \(\:h\) , \(\:c\) , and \(\:{k}_{B}\) are the Planck constant, the speed of light, and the Boltzmann constant, respectively. \(\:{I}_{\text{A}\text{M}1.5}\) denotes the standard AM1.5G solar spectral irradiance. The convection heat transfer coefficient is represented by ​ \(\:{h}_{c}\) , while conductive heat loss is neglected owing to the thermal insulation provided by the polystyrene foam enclosure. For the SH layer, the net radiative heating power is obtained by reversing the sign of \(\:{P}_{\text{n}\text{e}\text{t}}\) . Declarations Acknowledgement This work was supported by the National Research Foundation of Korea (Grant numbers: RS-2024-00448499, RS-2024-00343512). Conflict of Interest The authors declare no conflict of interest. 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Sensors 24:4793 Additional Declarations There is NO Competing Interest. Supplementary Files SupplementaryInformationFinal.docx Supplementary information SupportingInformationlegends.docx Antigravitymoisturetransportcombined.mp4 Anti-gravity moisture transport Gravitymoisturetransport.mp4 Gravity moisture transport Cite Share Download PDF Status: Under Review Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8884215","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":593442669,"identity":"ed9df9e6-d7ac-456e-ae0c-ccb896138d9c","order_by":0,"name":"Jinwoo Lee","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA2UlEQVRIiWNgGAWjYBACxnYgIVHBJsdwACJgQFhLM5CwOMNnTLwWBmYgrmyTS2wgWgtzM/PBBzfOmKX3nV9jwPCjhsHYvIGgw9iSDWdUpOXOvPHGgLHnGIOZzAGCWnjMpCXOHMvdcOOMAQNvA4ONBCGHMTbzf//9t+1/ugFQC+Nf4rTwsDFItrElGJzvMWAG2mJGhBY2YwmJM2yGM2+wFRyWOSZhTFCLYXvzww/AqJTnO39448M3NTaGMwhqaYCxJBJAsUnQDgYGeTiL/wBh1aNgFIyCUTAyAQB+7z7PiSNNOwAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0001-6344-5195","institution":"Dongguk University","correspondingAuthor":true,"prefix":"","firstName":"Jinwoo","middleName":"","lastName":"Lee","suffix":""},{"id":593442670,"identity":"a1b020d7-4366-4d54-b5be-6cb04f16748b","order_by":1,"name":"Seung Hwan Ko","email":"","orcid":"https://orcid.org/0000-0002-7477-0820","institution":"Seoul National University","correspondingAuthor":false,"prefix":"","firstName":"Seung","middleName":"Hwan","lastName":"Ko","suffix":""},{"id":593442671,"identity":"1d81cd65-5c51-481b-a956-8b40941c26ca","order_by":2,"name":"Yeongju Jung","email":"","orcid":"","institution":"Kookmin University","correspondingAuthor":false,"prefix":"","firstName":"Yeongju","middleName":"","lastName":"Jung","suffix":""},{"id":593442672,"identity":"44aa811e-6e74-4a48-a142-089645c9317d","order_by":3,"name":"Dong Hyun Kim","email":"","orcid":"","institution":"Dongguk University","correspondingAuthor":false,"prefix":"","firstName":"Dong","middleName":"Hyun","lastName":"Kim","suffix":""},{"id":593442673,"identity":"0e3ad514-e111-4b5c-bfa1-ad80be7d6ab7","order_by":4,"name":"Farooq Khan","email":"","orcid":"","institution":"Dongguk University","correspondingAuthor":false,"prefix":"","firstName":"Farooq","middleName":"","lastName":"Khan","suffix":""},{"id":593442674,"identity":"8e39357a-a74c-4450-9be5-ce2c3dada1df","order_by":5,"name":"In Chul Shin","email":"","orcid":"","institution":"Dongguk University","correspondingAuthor":false,"prefix":"","firstName":"In","middleName":"Chul","lastName":"Shin","suffix":""},{"id":593442675,"identity":"42387597-7eaa-4a1d-9d45-4a3bbb646aab","order_by":6,"name":"Jeuk Lee","email":"","orcid":"","institution":"Dongguk University","correspondingAuthor":false,"prefix":"","firstName":"Jeuk","middleName":"","lastName":"Lee","suffix":""},{"id":593442676,"identity":"bdf8afbc-06a3-4a13-8f41-73cb7acb248f","order_by":7,"name":"Taeho Yoo","email":"","orcid":"","institution":"Dongguk University","correspondingAuthor":false,"prefix":"","firstName":"Taeho","middleName":"","lastName":"Yoo","suffix":""},{"id":593442677,"identity":"c65784df-90dd-4f62-ac8f-b05b9714cbe7","order_by":8,"name":"Jinwoo Na","email":"","orcid":"","institution":"Dongguk University","correspondingAuthor":false,"prefix":"","firstName":"Jinwoo","middleName":"","lastName":"Na","suffix":""}],"badges":[],"createdAt":"2026-02-15 06:55:23","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8884215/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8884215/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":103398208,"identity":"4aec20b1-27e3-4b54-892b-27660a0c2e3b","added_by":"auto","created_at":"2026-02-25 08:59:12","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":96921287,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eOverview of the device architecture and its operating mechanism. a\u003c/strong\u003eOverall schematic of the device architecture that shows stacked functional substrates and an integrated thermoelectric module. Device inversion enables switching between cooling and heating modes. \u003cstrong\u003eb \u003c/strong\u003ePhotographs of the fabricated device, showing top and side views. \u003cstrong\u003ec \u003c/strong\u003eGraphic illustration of the four operating modes and the associated heat-transfer mechanisms, in which a specific mode can be selected according to weather conditions. \u003cstrong\u003ed\u003c/strong\u003eOperating mechanisms and configurations of each thermoregulatory mode, describing the dominant heat and mass transfer pathways. \u003cstrong\u003ee\u003c/strong\u003e Expected energy consumption and associated heat-transfer mechanisms for each mode required to maintain skin temperature within the thermal comfort zone, for conventional and proposed devices.\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-8884215/v1/e9687b5c79921b2669cb7a49.png"},{"id":103398166,"identity":"8d2f87fa-12af-4be3-b087-27d75231ec51","added_by":"auto","created_at":"2026-02-25 08:59:02","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":766394,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eOptical and fluid transporting properties of SH-EC and RC layers. a\u003c/strong\u003e Photographs and SEM images of the SH-EC and RC layers that show representative surface morphologies and microstructural features. \u003cstrong\u003eb\u003c/strong\u003e Spectral reflectivity (visible–near-infrared) and emissivity (infrared) of the SH-EC and RC layers, demonstrating their optical selectivity across relevant wavelength ranges. \u003cstrong\u003ec\u003c/strong\u003eCalculated cooling power of the RC layer and heating power of the SH-EC layer at convective heat-transfer coefficients (\u003cem\u003eh\u003c/em\u003e) of 0, 2, 4, 6, and 8 W m⁻² K⁻¹ under an ambient temperature of 300 K. \u003cstrong\u003ed\u003c/strong\u003e Schematic of the outdoor testing configuration and a photograph of the sky conditions on the testing day. \u003cstrong\u003ee\u003c/strong\u003e Outdoor testing results that provide solar irradiance (top) and corresponding sample temperature responses (bottom) as a function of time. \u003cstrong\u003ef\u003c/strong\u003ePore-size distributions of the hydrophobic and hydrophilic layers and their corresponding water contact angles, demonstrating asymmetric wettability and hierarchical porosity. \u003cstrong\u003eg\u003c/strong\u003e Schematic illustration of the evaporative cooling mechanism driven by capillary transport and pore-size contrast in the bilayer membrane. \u003cstrong\u003eh\u003c/strong\u003e Moisture-transport demonstration that explains directional liquid transport. A droplet applied to the hydrophobic side (top) penetrates the membrane and wets the hydrophilic surface, whereas a droplet applied to the hydrophilic side (bottom) spreads laterally without penetrating the membrane. \u003cstrong\u003ei\u003c/strong\u003e Moisture management test results, showing a one-way transport index of 626%. \u003cstrong\u003ej\u003c/strong\u003e Time-dependent mass change during a gravimetric evaporation test (mass vs. time), quantifying evaporation kinetics under controlled conditions. \u003cstrong\u003ek\u003c/strong\u003e Average skin temperature as water evaporates from artificially simulated skin. \u003cstrong\u003el\u003c/strong\u003e Evaporation rate estimated from a transient droplet-evaporation test.\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-8884215/v1/a3f56ec718c61bc025dd53e3.png"},{"id":103398206,"identity":"09c3d702-c5fb-4607-b986-39a0254ace05","added_by":"auto","created_at":"2026-02-25 08:59:11","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":81228790,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eActive thermoelectric cooling/heating characterization. a\u003c/strong\u003e Photographs of the fully assembled device demonstrating mechanical flexibility and stretchability under bending and tensile deformation. \u003cstrong\u003eb\u003c/strong\u003e Thermal conductivity of elastomer composites with and without BN incorporation measured by laser flash analysis, demonstrating enhanced heat conduction upon conductive filler integration. \u003cstrong\u003ec\u003c/strong\u003eThermal conductivity of elastomer composites with and without GNP incorporation. \u003cstrong\u003ed\u003c/strong\u003e Illustration of a finger contacting substrates with and without BN incorporation under active thermoelectric heating. Left panels show spatial temperature distributions at the contact interface. \u003cstrong\u003ee\u003c/strong\u003eIllustration of a finger contacting substrates with and without GNP incorporation under active thermoelectric cooling. Left panels show spatial temperature distributions at the contact interface. \u003cstrong\u003ef\u003c/strong\u003e Thermoelectric heating performance during skin contact under applied voltages in the range between 1.0 and 1.5 V, including corresponding skin-temperature time profiles. \u003cstrong\u003eg\u003c/strong\u003eThermoelectric cooling performance during skin contact under applied voltages in the range between -1.0 and -2.0 V, including corresponding skin-temperature time profiles. \u003cstrong\u003eh\u003c/strong\u003e Normalized resistance change as tensile strain increases from 0% to 140%. \u003cstrong\u003ei\u003c/strong\u003e Normalized resistance change during cyclic stretching at 30% tensile strain. The inset figure corresponds to the magnified view of the normalized resistance in the course of cyclic stretching. \u003cstrong\u003ej\u003c/strong\u003eInfrared images of normal (top) and stretched (bottom) states during thermoelectric heating. \u003cstrong\u003ek\u003c/strong\u003e Infrared images of normal (top) and stretched (bottom) states during thermoelectric cooling.\u003c/p\u003e","description":"","filename":"Figure3.png","url":"https://assets-eu.researchsquare.com/files/rs-8884215/v1/1d1045ddc40cb51e7df6db05.png"},{"id":103398207,"identity":"4b8f2a3d-27cb-4ada-9125-0c2891394ed4","added_by":"auto","created_at":"2026-02-25 08:59:12","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":96143333,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eEnergy efficiency and heat-transfer evaluation of the fully assembled thermoregulatory wearable. a\u003c/strong\u003eMultiphysics simulation of the proposed device attached to a skin model that delivers the time-dependent temperature change of skin/device interface (top) and the corresponding electrical power consumption over time (bottom) under extremely hot and cold ambient conditions while maintaining a target skin temperature at 35 °C. \u003cstrong\u003eb\u003c/strong\u003e Multiphysics simulation of a conventional thermoelectric device attached to the same skin model, presenting the temperature change (top) and power consumption over time (bottom) under identical extreme ambient conditions with a 35 °C target. \u003cstrong\u003ec\u003c/strong\u003e Estimated energy consumption of the proposed device and the conventional thermoelectric device after 10 min of device operation. \u003cstrong\u003ed\u003c/strong\u003e Experimental demonstration of active cooling using the fabricated device on an artificially simulated skin under extremely high ambient temperature conditions. \u003cstrong\u003ee\u003c/strong\u003e Experimental demonstration of active heating using the fabricated device on an artificially simulated skin under extremely low ambient temperature conditions. \u003cstrong\u003ef\u003c/strong\u003ePassive operation of the fabricated device on simulated skin under RC-up configurations, accompanied by the corresponding ambient temperature conditions. \u003cstrong\u003eg\u003c/strong\u003e Passive operation of the fabricated device on simulated skin under SH-up configurations, along with the corresponding ambient temperature conditions. \u003cstrong\u003eh\u003c/strong\u003e Comparison of temperature reduction on simulated skin between RC-only and RC+EC configurations, demonstrating the additional EC cooling. The dotted vertical lines indicate the time when water was applied to the device surface. \u003cstrong\u003ei\u003c/strong\u003e Infrared thermography images acquired from 100-1000 s during the outdoor validation test, visualizing transient surface-temperature evolution. The inset figure captures a schematic of the infrared thermography–based outdoor validation test setup for bare skin, SH mode, and RC mode. For bare skin measurements, the thermocouple was fixed using polyimide adhesive. \u003cstrong\u003ej\u003c/strong\u003e Time-dependent temperature difference extracted from the outdoor IR thermography test (Fig. i), quantifying the cooling/heating response over the measurement duration.\u003cstrong\u003e k\u003c/strong\u003e Photograph of a human subject wearing clothing integrated with a 2 × 2 array of devices in heating mode. \u003cstrong\u003el\u003c/strong\u003ePhotograph of a human subject wearing clothing integrated with a 2 × 2 array of devices in cooling mode.\u003c/p\u003e","description":"","filename":"Figure4.png","url":"https://assets-eu.researchsquare.com/files/rs-8884215/v1/d7b2abe806bd501806d84067.png"},{"id":103398179,"identity":"c8e67cba-e1be-4750-a508-ae62ef8bde7c","added_by":"auto","created_at":"2026-02-25 08:59:09","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1711477,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8884215/v1/96e3c83d-7b5c-4bdd-85e7-c6eaaabacb1f.pdf"},{"id":103398209,"identity":"74c83da3-0c22-466b-a55c-852fb1c24deb","added_by":"auto","created_at":"2026-02-25 08:59:12","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":5903302,"visible":true,"origin":"","legend":"Supplementary information","description":"","filename":"SupplementaryInformationFinal.docx","url":"https://assets-eu.researchsquare.com/files/rs-8884215/v1/067d4ff3816b7cb6c579f028.docx"},{"id":103398165,"identity":"b99f29b9-7131-4fa7-8360-3b23483e1396","added_by":"auto","created_at":"2026-02-25 08:59:02","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":13984,"visible":true,"origin":"","legend":"","description":"","filename":"SupportingInformationlegends.docx","url":"https://assets-eu.researchsquare.com/files/rs-8884215/v1/20f892e3cad40f1e1ffa2f2d.docx"},{"id":103398167,"identity":"39315eae-f495-439f-93d5-72e2d91ecbbf","added_by":"auto","created_at":"2026-02-25 08:59:03","extension":"mp4","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":12245885,"visible":true,"origin":"","legend":"Anti-gravity moisture transport","description":"","filename":"Antigravitymoisturetransportcombined.mp4","url":"https://assets-eu.researchsquare.com/files/rs-8884215/v1/712e900e5efb643c89baab78.mp4"},{"id":103398205,"identity":"6d03a14a-bfe1-4190-a89d-c7decf035f93","added_by":"auto","created_at":"2026-02-25 08:59:11","extension":"mp4","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":51983508,"visible":true,"origin":"","legend":"Gravity moisture transport","description":"","filename":"Gravitymoisturetransport.mp4","url":"https://assets-eu.researchsquare.com/files/rs-8884215/v1/0f55fbb559b4d0e50f7a5179.mp4"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Adaptable personalized thermoregulation through rational design of passive and active heat transfer","fulltext":[{"header":"Introduction","content":"\u003cp\u003eAs global climate change accelerates, extreme weather events, such as prolonged heat waves and cold spells, pose serious threats to human health and well-being. In this regard, effective thermoregulation not only preserves thermal comfort but also addresses a critical issue in public healthcare. Prolonged exposure to elevated or depressed temperature is directly associated with increased risks of heatstroke, hypothermia, cardiovascular strain, and even mortality, particularly among thermally vulnerable populations such as the elderly or outdoor workers \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. For instance, in 2025, the exceptional heatwave in Spain recorded 1,180 heat-related deaths, which was more than ten times higher than in the same period in 2024, highlighting the severe mortality risks posed by recent extreme climate events \u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e,\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eDespite growing attention to personal thermal regulation, previous thermal management technologies remain limited in their energy-efficiency. Active thermal devices, such as thermoelectric (TE) modules, offer promising solutions for wearable active thermal regulation strategies, owing to their ability to provide both cooling and heating within a single architecture. Recent advances in materials science and engineering have enabled the implementation of TE devices in human-centric wearable designs, improving stretchability and wearing comfort for continuous use \u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e,\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e. Nevertheless, TE-based systems rely exclusively on externally supplied electrical power to induce thermal modulation, which fundamentally constrains their energy efficiency and poses a significant challenge for sustainable wearable applications \u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eIn this regard, passive heat-transfer strategies, including radiative cooling (RC), evaporative cooling (EC), and solar heating (SH), have attracted considerable interest as zero-energy approaches to personal thermal management \u003csup\u003e\u003cspan additionalcitationids=\"CR7\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e. However, these methods typically operate in a single thermal mode and strongly depend on ambient environmental conditions. As a result, their limited heat-transfer capacity produces insufficient power to regulate body temperature, as they rely on passive mechanisms, particularly under extreme weather conditions. In summary, both active and passive thermal devices fall short of offering a viable solution for supporting thermal homeostasis in real-world scenarios. Therefore, a rational integration of passive and active thermoregulatory strategies is essential to achieve energy-efficient, adaptable thermal regulations. Despite this need, to the best of the authors\u0026rsquo; knowledge, no prior study has demonstrated thermoregulatory wearables that seamlessly integrate (i) radiative and evaporative cooling, (ii) photothermal solar heating, (iii) active thermoelectric cooling, and (iv) heating within a single reconfigurable platform. Although TE systems incorporating RC or SH have been reported, these efforts have predominantly focused on energy harvesting or power generation\u003csup\u003e\u003cspan additionalcitationids=\"CR10\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e. As such, their design principles, performance metrics, and operational objectives are fundamentally different from those required for human-centered thermoregulation.\u003c/p\u003e \u003cp\u003eHere, we present an energy-efficient, personalized thermoregulatory wearable that rationally integrates passive and active heat transfer modes within a single platform, delivering adaptive temperature control in all-weather conditions. Unlike existing devices that rely exclusively on either active or passive heat-transfer mechanisms, this study combines both into an all-in-one system with distinct cooling and heating modes. The device enables passive thermal regulation under mild conditions and switches to an integrated mode that synergistically couples passive and active thermoelectric control under extreme environments, while reversible operation allows bidirectional temperature modulation. The device comprises two opposing functional layers, which are integrated across a TE module: a hexagonal boron nitride (h-BN)-elastomer composite layer for RC \u003csup\u003e12,13\u003c/sup\u003e, and an electrospun graphene-thermoplastic polyurethane (TPU) nanofiber membrane for broadband solar absorption and directional sweat evaporation\u003csup\u003e\u003cspan additionalcitationids=\"CR15\" citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e. Notably, EC is incorporated into the SH layer, as this layer interfaces directly with the skin during cooling operation. To facilitate efficient EC in the SH layer, we engineered a wettability gradient across the membrane thickness to enable capillary-driven moisture uptake at the skin interface \u003csup\u003e\u003cspan additionalcitationids=\"CR18\" citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e. Lastly, for bidirectional thermoelectric temperature modulation, we employed the passive layers as substrates and soldered an array of Bi\u003csub\u003e2\u003c/sub\u003eTe\u003csub\u003e3\u003c/sub\u003e thermoelectric legs on top of interconnecting serpentine Cu electrodes\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e,\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e. As a result, during active TE modulation, passive heat transfer takes place alongside the active mode, enhancing thermoregulation and reducing energy consumption. Especially, through combined theoretical simulations and experimental validation, we demonstrate an energy-efficient thermoregulation strategy across diverse climatic conditions. In this regard, by integrating passive and active thermoregulation with bidirectional functionality in a single device for the first time, this work advances future wearable thermal technologies that can sustain human comfort in extreme climates while reducing energy demand.\u003c/p\u003e"},{"header":"Results \u0026 discussion","content":"\u003cp\u003e \u003cb\u003e2.1 Overview of the device architecture and its operating mechanism\u003c/b\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea provides a graphical illustration of the structural design, which is rationally engineered to adaptively regulate skin temperature through invertible orientation for reversible cooling and heating. The overall device comprises RC and SH-EC layers, which are positioned on opposite sides of vertically stacked thermoelectric legs. The TE layer consists of a \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:10\\times\\:10\\)\u003c/span\u003e\u003c/span\u003e array of vertically aligned Bi\u003csub\u003e2\u003c/sub\u003eTe\u003csub\u003e3\u003c/sub\u003e legs, which are soldered to laser-patterned serpentine copper electrodes. In the heating mode (H-mode), the SH layer faces up and absorbs incident solar radiation, which is transferred through the TE module to warm the skin-contact side. Conversely, in the cooling mode (C-mode), the RC layer is oriented upward to reflect incident sunlight, while enabling thermal radiation to the sky and heat extraction from the body through the TE legs. Simultaneously, the SH-EC layer in contact with the skin wicks sweat away from the skin toward the exterior, generating a synergistic EC effect. Notably, although EC might intuitively be incorporated into the RC layer, it is instead deliberately integrated into the SH layer. This design choice is based on the device configuration in cooling mode, in which the SH layer is in direct contact with the skin and therefore directly governs moisture exchange with the body. Accordingly, hydrophobic and hydrophilic bilayers constitute the SH-EC layer to facilitate unidirectional fluid transport, ensuring effective EC when the RC layer faces the sky. Based on this rationally designed architecture, the user can switch between operating modes simply by flipping the device. When passive SH or RC/EC alone is insufficient, the TE module provides active heating or cooling to maintain the target temperature. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb shows the corresponding top and side views of the device for each mode.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo elaborate on each heat transfer mode in detail, Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec delineates four distinctive modes: (i) integrated heating mode, (ii) eco-heating mode, (iii) eco-cooling mode, and (iv) integrated cooling mode. The integrated heating mode synergistically combines SH and TE heating, delivering intense heating to regulate body temperature in extremely cold weather (Mode 1). On the other hand, the eco-heating mode utilizes SH to provide moderate thermal output without electrical power consumption, making it suitable for mildly cold conditions (Mode 2). Similarly, the eco-cooling mode relies on RC and EC to produce mild cooling without external energy input (Mode 3), whereas the integrated cooling mode enhances the cooling performance by incorporating TE cooling, enabling effective thermoregulation under extreme heat conditions (Mode 4). Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed illustrates a schematic summary of the operational modes and the associated heat-transfer mechanisms under solar irradiation.\u003c/p\u003e \u003cp\u003eFrom an energy consumption perspective, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee, SH, RC, and EC operate through passive heat transfer mechanisms that require no electrical input, thereby obviating the additional amount of energy needed to achieve thermal comfort under mildly chilly or warm environmental conditions. Besides, even under extremely cold or hot conditions, the incorporation of these passive heat transfer mechanisms substantially reduces the overall energy required to reach the thermal comfort zone when compared with conventional thermoelectric devices that rely solely on active heat transfer. Consequently, the rational integration of passive and active heat transfer mechanisms enhances energy efficiency while maintaining effective thermal regulation across a wide range of environmental conditions, surpassing the limitations of conventional thermal management strategies. The detailed validation based on theoretical calculations is discussed in the following section.\u003c/p\u003e \u003cp\u003e \u003cb\u003e2.2 Optical properties of SH-EC and RC layers\u003c/b\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea shows actual photographs of the SH-EC and RC layers, along with scanning electron microscopy (SEM) images of their microstructures in the inset figure. Since we electrospun the SH-EC film, it consists of a nanofiber network with varying pore sizes, whereas the RC layer shows a flat, non-porous microsurface, as it was made by mold-casting. \u003cb\u003eSupplementary Fig.\u0026nbsp;1\u003c/b\u003e presents cross-sectional SEM images of the SH-EC layer, which clearly show a bilayer structure consisting of hydrophilic and hydrophobic layers. To evaluate the optical properties of each layer, we conducted spectroscopic characterization on the RC and SH-EC films using ultraviolet-visible-near-infrared (UV-Vis-NIR) and Fourier transform infrared (FTIR) spectroscopy, as presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb. The SH-EC layer exhibits a low broadband reflectance of 13.4% over 300\u0026ndash;2500 nm, indicating strong solar absorption (86.6% absorption) by the embedded graphene nanoplatelets (GNPs). The near-zero bandgap of graphene enables broadband interband absorption across the solar spectrum. Meanwhile, the nanoplatelet morphology increases the effective optical path length through multiple light-scattering events, which serve to further suppress reflectance. \u003csup\u003e15,22\u003c/sup\u003e Also, we selected TPU as the electrospinning matrix due to its high solution processability, elasticity, and ability to form mechanically robust fibrous networks with tunable wettability \u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e,\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e. In contrast, the RC layer consisted of a h-BN/Ecoflex composite, designed for high solar reflectivity and mid-infrared emissivity. h-BN possesses a wide bandgap (\u0026asymp;\u0026thinsp;5.9 eV) and strong phonon-polariton resonances in the 8\u0026ndash;13 \u0026micro;m atmospheric window, making it ideally suited for RC applications \u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e. When randomly dispersed within the Ecoflex matrix, h-BN nanoplatelets induce strong multiple-scattering effects, further enhancing broadband solar reflection. Furthermore, we deliberately employed nanoplatelet-shaped h-BN to maximize RC performance by promoting anisotropic scattering and increased optical path lengths \u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e. Spectral analysis showed reflectance of 95.8% across the solar spectrum, and the FTIR results confirmed a mid-IR emissivity of 92.3%. We calculated the emissivity based on Kirchhoff\u0026rsquo;s law, which stipulates that for opaque bodies in thermal equilibrium, the spectral emissivity equals spectral absorptivity (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\epsilon\\:=1-\\text{R}\\)\u003c/span\u003e\u003c/span\u003e) \u003csup\u003e27\u003c/sup\u003e. These optical characteristics enable the RC film to reflect incoming solar radiation while efficiently dissipating internal heat to the sky, promoting RC. Based on the optical results of SH-EC and RC layers, we theoretically calculated the cooling and heating power of each layer with rising convective heat-transfer coefficient (\u003cem\u003eh\u003c/em\u003e) in the range from 0 to 8 W\u0026middot;m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u0026middot;K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e with an increment of 2 W\u0026middot;m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u0026middot;K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at the ambient temperature of 300 K. The result shows that the cooling and heating power of RC and SH-EC films corresponds to 81.7 W\u0026middot;m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and 732.8 W\u0026middot;m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec\u003cb\u003e)\u003c/b\u003e. The detailed data for calculations is presented in \u003cb\u003eSupplementary Fig.\u0026nbsp;2\u003c/b\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo validate passive performance under real-life conditions, we performed an outdoor field test (September 26th, 2025, in Seoul, South Korea) using the experimental setup as in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed. To isolate the samples from environmental thermal effects, we placed the RC and SH-EC samples on an insulation box to minimize conduction and added an aluminum foil lining to reduce heat transfer from exterior radiation. We also recorded the sample and ambient temperature with separate thermocouples housed inside the windshield to diminish the effect of air convection (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee). Relative to the ambient temperature, the RC film remained sub-ambient for most of the experimental period, with average and maximum temperature differences of 2.55\u0026deg;C and 8.0\u0026deg;C, respectively. By contrast, the SH film exhibited strong solar-driven heating with mean temperature difference of 11.45\u0026deg;C, achieving a maximum super-ambient rise of 24.6\u0026deg;C. Notably, although earlier studies primarily relied on wind-shielded conditions \u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e, recent investigations have increasingly considered airflow to better approximate real-world environments \u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e. Consistent with this approach and considering the intended practical use of the fully assembled device on human skin, we conducted outdoor experiments under airflow-exposed conditions (\u003cb\u003eSupplementary Fig.\u0026nbsp;3\u003c/b\u003e), offering the thermal management performance comparable to those reported in recent airflow-considered studies \u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e. Overall, these results corroborate the spectroscopic trends of the SH-EC and RC layers and confirm thermal functions under realistic outdoor conditions.\u003c/p\u003e \u003cp\u003e \u003cb\u003e2.3 Evaporative cooling performance and sweat managing function of the SH-EC film\u003c/b\u003e \u003c/p\u003e \u003cp\u003eApart from RC and TE cooling, we incorporated EC mode into the system by engineering the wettability across the membrane thickness. To attribute evaporative functionality to a wettability gradient, we employed electrospinning to deposit hydrophobic and hydrophilic layers on top of one another. The hydrophobic side of the membrane features loosely packed and coarse fibers, whereas the hydrophilic side exhibits finer fibers in a much denser network to promote unidirectional liquid transport from hydrophobic to hydrophilic sides \u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e,\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e. By controlling the pore size and surface chemistry of the electrospun membrane, the Laplace pressure can be engineered to drive liquid flow in one direction, as shown in the equation below:\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:\\varDelta\\:P=\\frac{2\\gamma\\:cos\\theta\\:}{r}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\gamma\\:\\)\u003c/span\u003e\u003c/span\u003e, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\theta\\:\\)\u003c/span\u003e\u003c/span\u003e, and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:r\\)\u003c/span\u003e\u003c/span\u003e correspond to surface tension, contact angle, and radius of the pore. Based on the equation, on the hydrophobic face, larger pores should minimize the initial barrier to fluid flow through, while smaller pores amplify capillary suction on the hydrophilic side. This creates a steep Laplace pressure drop across the membrane thickness, driving spontaneous unidirectional transport.\u003c/p\u003e \u003cp\u003eTo realize the effective liquid transport across the membrane, we first tailored the pore size on each side of the membrane. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef shows the pore size of hydrophobic and hydrophilic layers along with the snapshots of their water contact angle in the inset figure. After optimizing the electrospinning conditions to control the membrane pore structure, we obtained average pore diameters of 0.515 \u0026micro;m and 0.101 \u0026micro;m on the hydrophobic and hydrophilic sides of the membrane, respectively. In addition, \u003cb\u003eSupplementary Fig.\u0026nbsp;4\u003c/b\u003e shows SEM images of the hydrophobic and hydrophilic sides, which clearly exhibit distinct pore sizes and fiber architectures that contribute to the contrasting wettability of the layers. To further enhance the hydrophilicity, we incorporated an amphiphilic triblock copolymer (Pluronic F127) into the nanofiber matrix, as Pluronic F127 consists of functional PEO and PPO groups within its chains. Therefore, the PEO blocks form hydrogen bonds with water molecules while the PPO blocks anchor into the TPU fiber matrix, effectively converting the originally hydrophobic surface into a hydrophilic one. \u003cb\u003eSupplementary Fig.\u0026nbsp;5\u003c/b\u003e presents EDS images of the hydrophobic and hydrophilic layers, in which the hydrophilic side exhibits a higher oxygen-to-nitrogen (O/N) atomic ratio than the hydrophobic side due to the high oxygen content of F127. EDS analysis revealed O/N ratios of 3.02 and 2.09 for the hydrophilic and hydrophobic layers, respectively (\u003cb\u003eSupplementary Fig.\u0026nbsp;6\u003c/b\u003e). Using the collective effect of combining pore-size optimization with an amphiphilic triblock copolymer, we were able to engineer a pronounced wettability gradient across the membrane thickness. Water contact angle measurements confirmed this asymmetry: the hydrophobic surface exhibited a contact angle of 114.3\u0026deg;, while the hydrophilic surface showed a near-zero contact angle (\u0026asymp;\u0026thinsp;0\u0026deg;).\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eg explains the unidirectional fluid transport mechanism by using the wettability gradient across the membrane thickness. As the figure depicts, the water droplet can penetrate the bilayer membrane only at the hydrophobic surface because the smaller pores on this side generate a high threshold pressure that must be exceeded to initiate penetration. Once the droplet enters the membrane and reaches the hydrophilic region, the larger pores and strong capillary suction lower the hydraulic resistance and drive the liquid forward, preventing reverse flow from the hydrophilic to the hydrophobic side. On the other hand, if the water droplet enters the membrane from the hydrophilic side, the liquid initially wicks into the porous network due to strong capillary suction. However, once it approaches the hydrophobic region with smaller pores, the high breakthrough pressure prevents further penetration, causing the liquid to spread laterally on the adjacent hydrophilic region.\u003c/p\u003e \u003cp\u003eTo characterize the fluid transport mechanism, we conducted two complementary tests, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eh and \u003cb\u003eSupplementary Movie 1\u003c/b\u003e. The top sequence of images illustrates cross-plane capillary pumping: a dyed water droplet placed on the hydrophobic surface penetrates the membrane and is transported to the hydrophilic side within 9 s. In contrast, when the droplet is applied to the hydrophilic surface, only a negligible amount of liquid passes through the membrane, leading to spreading into the neighboring hydrophilic region. This asymmetric behavior follows Laplace pressure-driven transport, in which the wettability gradient determines the direction of liquid flow. \u003csup\u003e32,33\u003c/sup\u003e. Correspondingly, \u003cb\u003eSupplementary Fig.\u0026nbsp;7\u003c/b\u003e and \u003cb\u003eSupplementary Movie 2\u003c/b\u003e demonstrate the anti-gravity direction of fluid transport, in which the fluorescently dyed water is transported from the hydrophobic to the hydrophilic side against gravity due to capillary pumping. Yet, when water was applied to the hydrophilic side, the droplet spread laterally into the adjacent hydrophilic regions, corroborating unidirectional anti-gravity fluid transport. Along with evaporative cooling capability, the unidirectional fluid transporting function of the SH-EC layer facilitates sweat management during the C-mode, potentially enhancing the wear comfort. The moisture management tester (MMT) analysis in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ei further validates this directional transport behavior\u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e. The membrane exhibits a directional transport index (R) of 626%, which exceeds conventional moisture-wicking performance and indicates strong capillary pumping combined with effective barrier-layer functionality \u003csup\u003e\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eTo evaluate the evaporative cooling performance of the SH-EC layer, we conducted comparative drying experiments using commercially available textiles, including regular cotton and a moisture-wicking sports fabric (Nike Dri-FIT)\u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e. EC occurs as water molecules (or sweat) absorb latent heat from the SH-EC surface and undergo a phase change from liquid to vapor, thereby removing heat from the surface without increasing the temperature of the remaining liquid (\u003cb\u003eSupplementary Fig.\u0026nbsp;8\u003c/b\u003e). Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ej presents the temporal mass-loss profiles measured while each sample was placed on an artificial skin substrate maintained at 35\u0026deg;C via PID (Proportional-Integral-Derivative) temperature feedback control. In each test, 100 \u0026micro;L (0.1 g) of water at 66\u0026deg;C was dispensed onto the fabric surface, and the residual mass, \u0026#119898;(\u0026#119905;), was recorded under identical ambient conditions (22.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u0026deg;C). The SH-EC layer reached complete drying (\u0026#119898; = 0) within 8 minutes, whereas cotton and Dri-FIT required 30 and 31 minutes, respectively. These results indicate that the SH-EC layer enables markedly faster evaporation, primarily due to its rapid liquid-transport capability. Additionally, to verify the practical cooling effect of evaporative cooling, Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ek and \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003el compare evaporation rates and average skin temperatures with those of commercial fabrics. Using the identical experimental setup as previously, the evaporation event was identified by the characteristic cooling plateau followed by a rapid temperature rise, marking the transition to the dry state. From these intervals, we extracted the effective evaporation rates of 0.559 mL\u0026middot;h⁻\u0026sup1;, 0.400 mL\u0026middot;h⁻\u0026sup1;, and 0.123 mL\u0026middot;h⁻\u0026sup1; for the SH-EC layer, cotton, and Dri-FIT, respectively (ambient 22.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u0026deg;C). Similarly, the corresponding average skin temperatures during the evaporation period were 29.7\u0026deg;C, 30.1\u0026deg;C, and 28.9\u0026deg;C, respectively. In addition, we compared the cooling performance of each material in detail, as summarized in \u003cb\u003eSupplementary Fig.\u0026nbsp;9\u003c/b\u003e. Thus, these sequential results confirm that the SH-EC layer achieves the highest evaporation rate and cooling effect among the tested materials, demonstrating efficient capillary-driven liquid uptake and vapor transport.\u003c/p\u003e \u003cp\u003e \u003cb\u003e2.4 Active thermoelectric cooling/heating characterization\u003c/b\u003e \u003c/p\u003e \u003cp\u003eTo enable reversible, electrically driven thermal modulation, the device incorporates a π-type TE module, which is positioned between the RC and SH-EC layers. As thermoelectric leg materials, Bi\u003csub\u003e2\u003c/sub\u003eTe\u003csub\u003e3\u003c/sub\u003e was selected for its high thermoelectric figure of merit (zT\u0026thinsp;\u0026asymp;\u0026thinsp;1 near 300 K) and superior carrier mobility at skin-relevant temperatures, making it one of the most efficient inorganic TE materials for wearable applications \u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e,\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e. Each pellet, 2.5 mm in height, was soldered onto laser-cut serpentine copper interconnects using eutectic solder paste. This alloy provides low-melting-point processing (~\u0026thinsp;183\u0026deg;C) and excellent wetting behavior, while forming intermetallic compounds such as Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e and Cu\u003csub\u003e3\u003c/sub\u003eSn at the Cu-solder interface \u003csup\u003e\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e,\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e, which enhance thermal stability and electrical bonding strength. The serpentine Cu electrode accommodates mechanical deformation through in-plane stretching and buckling, maintaining stable electrical connectivity during flexing and bending \u003csup\u003e\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea presents the assembled device, showing the SH-EC and RC layers oriented upward when the device is bent or stretched.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn addition to providing RC, EC, and SH functionalities, we incorporated highly thermally conductive fillers into the elastomer to enhance thermal conductivity, consequently improving the efficiency of active heating and cooling in the module. We incorporated h-BN nanoparticles into Ecoflex for the RC layer and GNPs into TPU for the SH-EC layer. In addition to enabling the desired optical functionalities, the incorporation of these particles simultaneously enhances the thermal conductivity of each layer. Notably, most previous RC studies have relied on porous structures to achieve favorable optical properties. While such designs are effective in enhancing solar reflectance and mid-infrared emissivity, they generally suffer from low thermal conductivity, which limits their suitability for wearable applications that require efficient heat transfer. To address this limitation, we incorporated h-BN nanoparticles into the Ecoflex matrix, increasing the thermal conductivity to 0.471 W\u0026middot;m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026middot;K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, representing a 2.69-fold increase over the pristine elastomer (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). Similarly, for the SH-EC layer, a porous structure is inherently required to enable sweat evaporation, which would compromise thermal conductivity. To overcome this intrinsic trade-off, we introduced GNPs into the TPU matrix, boosting the thermal conductivity to 0.610 W\u0026middot;m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026middot;K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, representing a 2.10-fold increase relative to bare TPU. This strategy effectively addresses the thermal properties associated with porosity while preserving evaporative cooling functionality (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec).\u003c/p\u003e \u003cp\u003eTo validate the effect of thermal conductivity on heat transfer between the device and the human skin, we performed a Multiphysics numerical simulation for cases with and without thermally conductive fillers (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee). Thus, we computed the transient temperature response of the finger-tip interface with the device over a 300 s time window. It should be noted that heating and cooling were evaluated on both sides of the device, reflecting its intended wearable operation. Specifically, when heating the skin, the h-BN/Ecoflex RC layer is in contact with the skin, whereas for cooling, the SH-EC layer interfaces with the skin. Accordingly, for the h-BN/Ecoflex RC layer, TE heating was applied to evaluate heat transfer from the RC layer to the fingertip. At a device temperature of 50\u0026deg;C, the sample incorporating h-BN fillers exhibited a mean interface temperature that was 1.12\u0026deg;C higher than that of the pristine sample, corroborating enhanced heat-transfer efficiency. Conversely, for the SH-EC layer, TE cooling was employed to assess cooling performance at the skin interface. At a device temperature of 15\u0026deg;C, the sample achieved an average temperature reduction of 0.25\u0026deg;C, compared with the neat sample, demonstrating improved cooling effectiveness. Although these simulations assume idealized, complete thermal contact at the skin-device interface, the results clearly indicate that loading with thermally conductive fillers enhances heat transfer between the device and the skin. Such enhanced thermal transport can potentially reduce the electrical energy required to operate the TE module, because it can achieve the same level of heating or cooling with a lower electrical input.\u003c/p\u003e \u003cp\u003eTo demonstrate temperature controllability, we varied the applied voltage, as it directly modulates the TE cooling and heating output. For instance, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef depicts the time-dependent temperature response of the heating mode as the electrical input ranges from 1.0 V to 1.5 V in increments of 0.1 V, resulting in a temperature rise of 21.7\u0026deg;C at 1.5 V. The IR images in \u003cb\u003eSupplementary Fig.\u0026nbsp;10a\u003c/b\u003e illustrate the residual heating effect on the human hand after the TE device is removed. Similarly, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eg presents the TE cooling response, in which the applied voltage is varied from \u0026minus;\u0026thinsp;1.0 V to -2.0 V in 0.2 V, yielding temperature drops of up to 13.6\u0026deg;C. As in heating mode, cooling mode also leaves a residual cooling effect on the skin (\u003cb\u003eSupplementary Fig.\u0026nbsp;10b\u003c/b\u003e). These results confirm that both TE heating and cooling modes are capable of providing effective heat transfer at the skin surface, enabling sufficient control of body temperature.\u003c/p\u003e \u003cp\u003eSince wearable devices must withstand mechanical stresses associated with everyday use, we performed a series of mechanical durability tests to evaluate the fatigue strength of the device. \u003cb\u003eSupplementary Fig.\u0026nbsp;11a\u003c/b\u003e demonstrates the effect of varying bending radius on the normalized electrical resistance of the device over a range from the flat state to 4.5 mm. The results show negligible variation in normalized resistance with decreasing bending radius, indicating excellent mechanical robustness even under severe curvature. Additionally, as mechanical failure in practical applications typically originates from fatigue caused by repeated deformation, we further assessed the device's durability by monitoring the normalized resistance during cyclic bending with a bending radius of 3.5 mm. As shown in \u003cb\u003eSupplementary Fig.\u0026nbsp;11b\u003c/b\u003e, the normalized resistance remains nearly constant over 1000 bending cycles, confirming stable electrical performance under repeated mechanical loading. In addition to bending tests, tensile deformation experiments were performed to evaluate the device\u0026rsquo;s tolerance to stretching. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eh shows the normalized resistance as a function of tensile strain, increased incrementally by 10% up to a maximum strain of 140%. The resistance remains stable throughout the entire strain range, demonstrating reliable electromechanical stability even under large deformation. To further examine fatigue resistance under tensile loading, cyclic stretching tests were conducted at 30% tensile strain (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ei). Although minor fluctuations in resistance are observed during cycling, no mechanical failure or performance degradation occurs over 1000 stretching cycles, substantiating the mechanical robustness of the device under repeated mechanical loading associated with everyday wear. Furthermore, to verify the stable TE operation under mechanical deformation, we applied tensile strain of 30% to the device during active TE operation (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ej and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eh). When compared with the pristine device under no mechanical loading, the strained device exhibits comparable heat-transfer performance in both cooling and heating modes, corroborating that mechanical deformation does not significantly degrade TE functionality.\u003c/p\u003e \u003cp\u003e \u003cb\u003e2.5 Energy efficiency and heat transfer evaluation of fully assembled thermoregulatory wearable\u003c/b\u003e \u003c/p\u003e \u003cp\u003eTo demonstrate energy-efficient thermoregulatory operation, we numerically calculated the power required for the device to maintain skin temperature within the thermal comfort zone under arbitrary weather conditions and compared it with that of a conventional thermoelectric device (cTED) over 60 s. The temperature profiles in the top row of Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea show the time-dependent skin-device interface temperature when the device maintains skin temperature within the thermal comfort zone, along with the corresponding ambient temperatures under extreme and variable weather conditions. The bottom plots display the calculated power consumption required to achieve the observed thermoregulatory performance. In parallel, Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb presents the corresponding results obtained under identical weather conditions using cTED that relies solely on active TE heating and cooling. We excluded the effect of EC from numerical simulations because its cooling strength depends on the amount of water undergoing phase change, which varies with user-specific and environmental conditions and cannot be reliably prescribed in the model. Compared to the proposed device that employs passive, energy-free heat transfer under mild weather conditions, cTED requires 8.61 J and 63.1 J to reach the thermal comfort zone, respectively (\u003cb\u003eSupplementary Fig.\u0026nbsp;12\u003c/b\u003e). Moreover, even under conditions that necessitate active control, when compared to cTED, the integrated modes of the proposed device exhibit energy reductions of 2.13 J for cooling and 5.31 J for heating over a 60 s time window. This energy advantage becomes more pronounced as operation time increases. For example, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec, extending the operation time to 600 s yields energy savings of 6.60 J and 32.3 J for integrated cooling and heating, respectively. These savings correspond to reductions of 14.3% and 24.9% in total energy consumption enabled by the incorporation of passive heat-transfer modes.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eSupplementary Fig.\u0026nbsp;13\u003c/b\u003e provides the simulation-based temperature evolution for four different heat-transfer modes over 60 minutes of operation under identical boundary conditions. The simulation results indicate that the active heat-transfer modes reach the temperature extremes shortly after the onset of the TE operation. After the active modes approach the temperature extremes, the temperature response begins to plateau, with the temperatures at 60 min computed to be \u0026minus;\u0026thinsp;2.48\u0026deg;C and 53.8\u0026deg;C for the active TE cooling and heating modes, respectively. On the other hand, the passive heat-transfer modes exhibit a more gradual temperature change over time, resulting in temperatures of 8.21\u0026deg;C and 51.1\u0026deg;C at 60 min for RC and SH, respectively. The simulation results highlight the complementary roles of passive and active heat-transfer modes, wherein passive mechanisms provide gradual and energy-free thermal regulation, while active thermoelectric operation enables rapid response to temperature extremes and precise thermal control.\u003c/p\u003e \u003cp\u003eTo analyze the practical performance of the active heating and cooling modes, we experimentally simulated thermally harsh environments of 50\u0026deg;C and \u0026minus;\u0026thinsp;10\u0026deg;C on average and placed an artificial skin substrate in each environment. To emulate the thermal load of human skin, we applied electrical power (4 W) to silicone substrate to maintain 35\u0026deg;C at room temperature. In addition, a PID feedback controller was implemented to rapidly drive and maintain the temperature within the thermal comfort zone (35\u0026deg;C). \u003cb\u003eSupplementary Fig.\u0026nbsp;14\u003c/b\u003e illustrates the PID control architecture used for closed-loop temperature regulation of the TE device. For TE cooling mode (at 50\u0026deg;C on average), Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed shows that the device is capable of maintaining the temperature of the artificial skin within the thermal comfort zone (T\u003csub\u003ec\u003c/sub\u003e). The incorporation of PID feedback control allows the device to reach T\u003csub\u003ec\u003c/sub\u003e rapidly and regulate the artificial skin temperature within this range thereafter. Conversely, the bare artificial skin without thermal regulation stabilizes at an average temperature of 53\u0026ndash;54\u0026deg;C, as the applied electrical heating used to emulate metabolic heat generation adds to the imposed ambient temperature of 50\u0026deg;C. In contrast, Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee shows that, in a sub-zero environment, the temperature of the bare artificial skin decreases to 1\u0026ndash;2\u0026deg;C, which is a level that may induce hypothermia under prolonged exposure. On the other hand, the PID-controlled active heating mode raises the artificial skin temperature to the setpoint and subsequently maintains it within the thermal comfort zone.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef and \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eg describe the outdoor thermoregulatory performance of the device under passive heat-transfer operation by comparing its SH and RC functionalities with bare simulated skin without the device. Again, we used artificial skin to simulate the thermal load of human skin and monitored the temperature of each sample, along with solar irradiance, over 500 s. The passive cooling mode also demonstrated effective cooling, reducing the average skin temperature by 6.76\u0026deg;C and the maximum skin temperature by 8.50\u0026deg;C. In parallel, when the SH-EC side is faced upward, the average skin temperature increased by 6.33\u0026deg;C, with the maximum temperature of 8.10\u0026deg;C, when compared with the bare simulated skin. Furthermore, to assess EC performance, Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eh compares samples with and without the EC function using the experimental setup illustrated in the inset. Throughout the experiment, we applied 100 \u0026micro;L of water to samples with and without EC functionalities and monitored the temperature using two thermocouples: one positioned between the device and the simulated skin (T\u003csub\u003ed\u003c/sub\u003e), and the other attached directly to the simulated skin (T\u003csub\u003es\u003c/sub\u003e). The result indicates that the temperature (T\u003csub\u003es\u003c/sub\u003e - T\u003csub\u003ed\u003c/sub\u003e) drops rapidly when water is applied to the EC layer, whereas the sample without the EC layer does not experience a significant temperature reduction. It is estimated that 100 \u0026micro;L of water induces a temperature reduction of 4.3\u0026deg;C on average, and the EC capability effectively contributes to body temperature regulation under extremely hot conditions that induce perspiration.\u003c/p\u003e \u003cp\u003eTo examine the passive performance of the fully assembled device on actual human skin, we mounted the devices on the human forearm in two configurations, with the SH or RC side facing upward, as presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ei. To monitor temperature, the thermocouple was attached to the interface between the human skin and the device, and we used PI adhesive to secure the thermocouple to the bare skin. The IR images show each sample mode on the human forearm at 100 s and 1000 s, delineating mode-dependent passive heat transfer and enhanced thermoregulatory effects over prolonged durations. The time-course of the temperature difference between each mode and bare skin is presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ej, indicating that both solar heating and radiative cooling can induce a\u0026thinsp;~\u0026thinsp;2\u0026deg;C change in temperature. Lastly, to showcase the practical usage of the device in real life, we integrated the devices (4 devices in a 2\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\times\\:\\)\u003c/span\u003e\u003c/span\u003e2 array) into the commercial garment, showing that it can be inverted to switch between heating (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ek) and cooling mode (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003el).\u003c/p\u003e \u003cp\u003eOverall, the device achieves adaptive, personalized thermoregulation through a rational integration design of active TE control with passive SH, RC, and EC within a single wearable platform. By adaptively regulating skin temperature within the thermal comfort zone under extreme environmental conditions while minimizing energy consumption through passive operation, the system provides a practical route toward adaptive personal thermal management. In this regard, the proposed approach represents a significant advance over existing wearable thermal technologies by offering energy-efficient and practical personal thermoregulation in real-world settings.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThis work demonstrates an adaptive thermoregulatory wearable that integrates active and passive heat transfer modes into a single device, offering personalized thermal management across all-weather conditions. Rational integration of active TE modulation with passive heat transfer not only provides adaptive thermoregulation in diverse environmental conditions but also allows efficient energy operation by prioritizing passive modes and minimizing the energy consumption of thermoelectric heat transfer. Based on the optical properties, the cooling and heating powers in the RC and SH layers show 81.7 W\u0026middot;m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and 732.8 W\u0026middot;m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, respectively. The outdoor test results demonstrate the notable performance of the passive heat-transfer modes: under the RC mode, the device reduces the temperature by up to 8.0\u0026deg;C, whereas under the SH mode, it increases the temperature by up to 24.6\u0026deg;C. In addition, the wettability gradient design of the SH-EC layer enables sweat removal from the skin while suppressing backflow, thereby sustaining EC and improving interfacial moisture management. EC presents an evaporation rate of 0.601 mL/h, which is more than 3.4 times that of commercial sportswear. Based on these rational designs integrating with passive heat transfer mechanisms and active TE modules, the numerical simulations demonstrated that, compared with the cTED, the integrated modes reduce energy consumption by 6.6 J and 32.3 J (comparable to the energy saving ratio of 14.3% and 24.9%) for cooling and heating, respectively, over a 600-s operation. In addition to theoretically simulated calculation, we experimentally validated that the final device maintains stable skin temperature within the comfort zone under mild to extreme environmental conditions. The PID-integrated TE heat transfer mode maintains the artificial skin temperature within the thermal comfort zone even under extreme thermal conditions of -10\u0026deg;C and 50\u0026deg;C. In contrast, under mild environmental conditions, passive thermal management alone maintains the thermal comfort zone without any energy input. Therefore, through comprehensive theoretical validation and experimental verification, the proposed system is clearly differentiated from prior wearable thermal technologies, offering a uniquely integrated, bidirectional, and energy-efficient strategy for personal thermal management. This work establishes a versatile design framework for next-generation wearable devices that is capable of maintaining thermal comfort across diverse environmental conditions while reducing energy demand and improving user comfort.\u003c/p\u003e"},{"header":"Experimental section","content":"\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eMaterials\u003c/h2\u003e \u003cp\u003eEcoflex 00\u0026ndash;30 (Parts A and B; Smooth-On; purchased from Hyupsin Mulsan, Republic of Korea) and Slo-Jo silicone thinner (Smooth-On; purchased from Hyupsin Mulsan, Republic of Korea) were used as the elastomer matrix for the radiative-cooling composite, with hexane (Daejin Sangsa, Republic of Korea) serving as the processing solvent. Hexagonal boron nitride (h-BN; average particle size\u0026thinsp;\u0026asymp;\u0026thinsp;1 \u0026micro;m, 98% purity; Sigma-Aldrich, Republic of Korea) was used as the radiative-cooling filler. Thermoplastic polyurethane (TPU; Shore 85A, pellet form; Sejin Poly, Republic of Korea) was employed as the polymer matrix for electrospinning. N,N-dimethylformamide (DMF, 99.0%; Daejin Sangsa, Republic of Korea) and methyl ethyl ketone (MEK, extra-pure grade; Daejin Sangsa, Republic of Korea) were used as electrospinning solvents. Graphene nanopowder (flake size\u0026thinsp;\u0026asymp;\u0026thinsp;12 nm; UNINANOTECH, Republic of Korea) was used as the photothermal filler. Pluronic F127 (Sigma-Aldrich, Republic of Korea) was incorporated to impart hydrophilicity to the skin-facing electrospun layer. Copper foil (25 \u0026micro;m thick, annealed, uncoated, 99.8% metals basis; Thermo Fisher Scientific, Republic of Korea) was used for electrodes and electrical interconnects. p- and n-type Bi₂Te₃ thermoelectric legs (99.99% purity; Wuhan Xinrong New Materials Co., Ltd., China) were used as the active thermoelectric elements. A rosin mildly activated (RMA) solder paste (Sn63/Pb37; AON CK, Republic of Korea) was used for solder bonding. Double-sided water-soluble tape (Navimro, Republic of Korea) was employed for temporary mounting during laser cutting.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eFabrication of Radiative-Cooling Layer (RC)\u003c/h3\u003e\n\u003cp\u003eThe RC composite film was prepared via solvent-assisted mixing and mold casting. Hexane, h-BN powder, Ecoflex Part A, Ecoflex Part B, and Slo-Jo were combined at a weight ratio of 7.5:3.3:2.5:2.5:0.05 (w/w). The mixture was stirred at 30\u0026deg;C (700 rpm, 10 min) to homogenize the dispersion and then degassed in a vacuum chamber for 3 min. The mixture was then cast into a mold and cured at 20\u0026deg;C for 12 h to obtain a stretchable RC composite film.\u003c/p\u003e\n\u003ch3\u003eFabrication of Solar-Heating Electrospun Layer (SH-EC)\u003c/h3\u003e\n\u003cp\u003eA vertically graded bilayer SH-EC membrane was fabricated by sequential electrospinning. For the hydrophobic sublayer, TPU containing graphene nanopowder (0.3 wt% relative to TPU solids) was dissolved in a mixed solvent of DMF and MEK (7:3 v/v) under stirring at 80\u0026deg;C until complete dissolution. The solution was electrospun onto a rotating collector at a flow rate of 0.5 mL h⁻\u0026sup1; under an applied voltage of 6 kV. Subsequently, a hydrophilic sublayer was formed by adding Pluronic F127 to TPU at a 10:1 (TPU:F127, w/w) ratio and electrospinning directly on the first layer at 1.0 mL h⁻\u0026sup1; under 8 kV. For both steps, the needle-to-collector distance was fixed at 10 cm.\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eDevice Interconnection and Integration\u003c/h2\u003e \u003cp\u003eAfter the RC layer was prepared, a copper foil was laminated onto the RC surface and patterned into the electrode layout by laser cutting. A solder mask was aligned to define the bonding pads, and solder paste was applied through the mask. Bi₂Te₃ thermoelectric legs (2.5 mm; alternating p- and n-type elements; 10 \u0026times; 10 array) were placed on the paste-defined pads and soldered on a hot plate at 230\u0026deg;C for 20 min. For the opposite-side electrode, a copper foil was temporarily mounted on a glass slide using double-sided water-soluble tape and laser-cut into a serpentine structure. The serpentine copper electrode was then soldered to complete the electrical interconnection under the same hot-plate condition (230\u0026deg;C for 20 min). After soldering, the assembly was allowed to cool to room temperature before lamination. Finally, the SH-EC layer was laminated onto the opposite side of the TE core, yielding a reversible thermal skin with RC and SH-EC layers on opposing faces. The entire fabrication process of assembled device is further elaborated in \u003cb\u003eFig. S14.\u003c/b\u003e\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eCharacterization\u003c/h3\u003e\n\u003cp\u003eUV\u0026ndash;vis\u0026ndash;NIR spectra were acquired using a JASCO V-770 spectrophotometer over 190\u0026ndash;2700 nm. FTIR spectra were collected using a Bruker VERTEX 70v spectrometer. Static water contact angles were measured using a KR\u0026Uuml;SS DSA100 goniometer. Surface morphology was examined by field-emission scanning electron microscopy (FE-SEM; TESCAN CLARA LMH), and elemental analysis was performed by energy-dispersive X-ray spectroscopy (EDS) coupled to the SEM. Moisture management behavior was evaluated using a moisture management tester (SDL Atlas M290). Infrared thermography and transient temperature responses were recorded using an IR camera (FLIR A35; 45\u0026deg; field of view; 60 Hz).\u003c/p\u003e\n\u003ch3\u003eCalculation of cooling/heating power\u003c/h3\u003e\n\u003cp\u003eBy applying the principle of energy conservation to the control volume surrounding the RC layer, the net radiative cooling power can be expressed as:\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e\n$$\\:{P}_{\\text{n}\\text{e}\\text{t}}={P}_{\\text{r}\\text{a}\\text{d}}-{P}_{\\text{a}\\text{t}\\text{m}}-{P}_{\\text{s}\\text{u}\\text{n}}-{P}_{\\text{n}\\text{o}\\text{n}-\\text{r}\\text{a}\\text{d}}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eAccording to Kirchhoff\u0026rsquo;s law, the spectral emissivity is equal to the spectral absorptivity. Using the experimentally measured emissivity spectrum of the sample, each term can be evaluated as follows.\u003c/p\u003e \u003cp\u003eThe radiative power emitted from the surface is given by:\u003cdiv id=\"Equc\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equc\" name=\"EquationSource\"\u003e\n$$\\:{P}_{\\text{r}\\text{a}\\text{d}}={\\int\\:}_{0}^{2\\pi\\:}{\\int\\:}_{0}^{\\pi\\:/2}{\\int\\:}_{0}^{\\infty\\:}{I}_{bb}\\left(T,\\lambda\\:\\right)\\epsilon\\:\\left(\\lambda\\:\\right)\\text{cos}\\theta\\:\\text{sin}\\theta\\:d\\lambda\\:d\\theta\\:d\\varphi\\:$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eThe absorbed solar radiation is calculated using the AM1.5G solar spectrum as:\u003cdiv id=\"Equd\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equd\" name=\"EquationSource\"\u003e\n$$\\:{P}_{\\text{s}\\text{u}\\text{n}}={\\int\\:}_{0}^{\\infty\\:}{I}_{\\text{A}\\text{M}1.5}\\left(\\lambda\\:\\right)\\epsilon\\:\\left(\\lambda\\:\\right)d\\lambda\\:$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eThe absorbed atmospheric thermal radiation is expressed as:\u003cdiv id=\"Eque\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Eque\" name=\"EquationSource\"\u003e\n$$\\:{P}_{\\text{a}\\text{t}\\text{m}}={\\int\\:}_{0}^{2\\pi\\:}{\\int\\:}_{0}^{\\pi\\:/2}{\\int\\:}_{0}^{\\infty\\:}{I}_{bb}\\left({T}_{\\text{a}\\text{t}\\text{m}},\\lambda\\:\\right)\\epsilon\\:\\left(\\lambda\\:\\right){\\epsilon\\:}_{\\text{a}\\text{t}\\text{m}}\\left(\\lambda\\:\\right)\\text{cos}\\theta\\:\\text{sin}\\theta\\:d\\lambda\\:d\\theta\\:d\\varphi\\:$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eNon-radiative heat exchange due to convection is described by:\u003cdiv id=\"Equf\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equf\" name=\"EquationSource\"\u003e\n$$\\:{P}_{\\text{n}\\text{o}\\text{n}-\\text{r}\\text{a}\\text{d}}={h}_{c}({T}_{\\text{a}\\text{t}\\text{m}}-T)$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:T\\)\u003c/span\u003e\u003c/span\u003e denotes the temperature of the sample and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{T}_{\\text{a}\\text{t}\\text{m}}\\)\u003c/span\u003e\u003c/span\u003e represents the atmospheric temperature. The spectral radiance of a blackbody is defined as:\u003cdiv id=\"Equg\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equg\" name=\"EquationSource\"\u003e\n$$\\:{I}_{bb}\\left(T,\\lambda\\:\\right)=\\frac{2h{c}^{2}}{{\\lambda\\:}^{5}\\left[\\text{exp}\\left(\\frac{hc}{\\lambda\\:{k}_{B}T}\\right)-1\\right]}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:h\\)\u003c/span\u003e\u003c/span\u003e, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:c\\)\u003c/span\u003e\u003c/span\u003e, and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{k}_{B}\\)\u003c/span\u003e\u003c/span\u003e are the Planck constant, the speed of light, and the Boltzmann constant, respectively. \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{I}_{\\text{A}\\text{M}1.5}\\)\u003c/span\u003e\u003c/span\u003e denotes the standard AM1.5G solar spectral irradiance. The convection heat transfer coefficient is represented by ​\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{h}_{c}\\)\u003c/span\u003e\u003c/span\u003e, while conductive heat loss is neglected owing to the thermal insulation provided by the polystyrene foam enclosure. For the SH layer, the net radiative heating power is obtained by reversing the sign of \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{P}_{\\text{n}\\text{e}\\text{t}}\\)\u003c/span\u003e\u003c/span\u003e.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the National Research Foundation of Korea (Grant numbers: RS-2024-00448499, RS-2024-00343512).\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003cstrong\u003eConflict of Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no conflict of interest.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eMora C et al (2017) Global risk of deadly heat. 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Sensors 24:4793\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-8884215/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8884215/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eAs extreme weather events become increasingly frequent and severe, sustaining thermal homeostasis under variable environmental conditions has become a growing challenge for maintaining thermal comfort and physiological stability. This study presents an energy-efficient, personalized thermoregulatory wearable that rationally integrates multimodal active and passive heat transfers to maintain human thermal comfort in all-weather conditions. The device offers a reversible operation in four distinctive modes: passive heat transfer through (i) radiative and evaporative cooling and (ii) solar heating, and active heat modulation through (iii) thermoelectric cooling and (iv) heating. The device employs an invertible, dual-sided architecture that enables switching between cooling and heating modes. Under mild weather conditions, the wearable maintains skin temperature within the thermal comfort zone through purely passive operation without external energy input. Under extreme conditions, it synergistically combines passive and active thermoregulation to sustain thermal comfort across ambient temperatures from \u0026minus;\u0026thinsp;10\u0026deg;C to 50\u0026deg;C. Compared with a conventional thermoelectric device, the proposed design reduces energy consumption by 14.3% and 24.9% for cooling and heating, respectively, during a 600-s operation. By adaptively offering both passive and active thermoregulatory modes, this work provides an energy-efficient strategy for personalized thermal management and effective thermal homeostasis in all-weather environments.\u003c/p\u003e","manuscriptTitle":"Adaptable personalized thermoregulation through rational design of passive and active heat transfer","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-25 08:58:47","doi":"10.21203/rs.3.rs-8884215/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-communications","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"NCOMMS","sideBox":"Learn more about [Nature Communications](http://www.nature.com/ncomms/)","snPcode":"","submissionUrl":"https://mts-ncomms.nature.com/","title":"Nature Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Communications","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"12d1e31d-ed9f-48e7-930b-522492d457bb","owner":[],"postedDate":"February 25th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":63149729,"name":"Physical sciences/Engineering/Mechanical engineering"},{"id":63149730,"name":"Physical sciences/Energy science and technology/Thermoelectric devices and materials"}],"tags":[],"updatedAt":"2026-03-17T03:56:03+00:00","versionOfRecord":[],"versionCreatedAt":"2026-02-25 08:58:47","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8884215","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8884215","identity":"rs-8884215","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}