Synergistically Reinforced Detachable Photonic Film for Efficient Daytime Radiative Cooling

ABSTRACT Radiative cooling is a passive thermal management strategy that reduces heat gain by reflecting solar energy and emitting infrared (IR) radiation through the atmospheric transparent window (ATW) corresponding to (8–13 µm), without energy consumption. In this study, we developed a mechanically robust, freestanding high‐performance radiative cooling composite film by dispersing silicon dioxide (SiO 2 ) and hexagonal boron nitride (h‐BN) into a polydimethylsiloxane (PDMS) matrix. The resulting SiO 2 ‐BN‐PDMS (SBP) film leverages a synergistic platelet‐sphere filler architecture, in which plate‐like h‐BN provides strong backscattering of solar light while spherical SiO 2 suppresses parasitic UV absorption and improves mechanical integrity at reduced filler loading. As a result, the composite film achieved a solar reflectance of up to 97.2% and an ATW emissivity up to 95.8%, enabling efficient passive radiative cooling under direct sunlight. Outdoor measurements demonstrated that the SBP film reduced surface temperature by 8.2°C below inner ambient conditions under direct sunlight. Furthermore, the film exhibits mechanical flexibility, hydrophobicity, and durability under thermal and weathering conditions, suggesting strong potential for applications in standalone cooling membranes for electronics cooling, and human protection in sun‐exposed environments.