Melt‐Processed, One‐Step, In Situ Hierarchically Structured Porous Polymer Nanocomposite for Radiative Cooling in Hot Weather

Abstract Porous polymeric composite materials have recently garnered significant attention for passive radiative cooling. However, challenges of solvent usage in pore formation and achieving uniform dispersion of nanoparticles in polymer matrix remain major obstacles in eco‐friendly construction of solar reflection/scattering structures. Here, porous polymer nanocomposites (FPCS) is presented with a hierarchically structured micropore/nanoparticle configuration, achieved by utilizing the thermal decomposition behavior of inexpensive sodium bicarbonate during universal melt processing. Sodium bicarbonate serves as micropore‐forming agent and providing a source of uniformly dispersed nanoparticles from thermally decomposed sodium carbonate. The fabrication process eliminates the need for solvents and facilitates the uniform dispersion of nanoparticles easily in polymer melts. FPCS demonstrates high solar reflectance (94.2%) and high mid‐infrared emissivity (94.5%), resulting in sub‐ambient daytime cooling of ≈6.8 °C and a promising cooling effect of ≈2.0 °C under hot weather with ambient temperatures exceeding 52 °C. Furthermore, FPCS enables efficient sub‐ambient cooling in environments with temperatures below zero. This study presents a straightforward, feasible, and eco‐friendly approach to producing high‐performance porous polymeric radiative cooling materials, showcasing significant potential for applications in building energy conservation, cooling water, preventing glacier melting, and addressing hot weather conditions.