Thermal Transport Engineering in an Adaptive Latent‐Radiative Hydrogel Thermostat

Hydrogel‐based thermal regulators have emerged as a critical strategy for passive heat management without active power consumption. The latent and radiative thermostat (LRT) has attracted particular attention owing to its ability to simultaneously exploit latent heat and radiative heat dissipation, enabling adaptive heat regulation by switching between heating and cooling modes. However, the inherently low thermal conductivity of organic materials fundamentally limits heat propagation from the heat source through the hydrogel matrix, constraining overall thermal regulation performance. To address this limitation, we demonstrate a thermally conductive latent and radiative thermostat (TCLRT) by incorporating calcium fluoride (CaF 2 ). CaF 2 particles combine relative transparency in visible regions with a refractive index close to those of the hydrogel constituents and relatively high thermal conductivity. The optimal TCLRT with 20% CaF 2 increased thermal conductivity from 0.471 to 0.533 W/m·K (13.2%), while retaining critical properties of LRT, including high infrared emittance, temperature‐dependent solar reflectance, and moisture‐regulating behavior. Outdoor measurements showed that TCLRT regulated the target object temperature more effectively than LRT under various tested conditions. These improvements reflect the combined effects of increased solar reflectance and thermal conductivity achieved through CaF 2 incorporation, together with the intrinsic LRT properties, such as transparency and latent‐heat‐based thermal regulation.