Durable and efficient passive daytime radiative cooling enabled by hierarchically porous polymer composites

Passive daytime radiative cooling offers an energy-free strategy for sustainable thermal management, yet maintaining long-term outdoor durability remains a major challenge for polymer-based emitters. Here, we report a durable hybrid cooling film based on a hierarchically porous poly(vinylidene fluoride-co-hexafluoropropylene) matrix incorporating a dual-functional ZrO 2 @potassium titanate (PT) hybrid filler. The high-refractive-index ZrO 2 enhances broadband solar reflection through strong dielectric scattering, while PT provides ultraviolet (UV) shielding via Ti–O coordination-mediated absorption and contributes to mid-infrared emission. Benefiting from the synergistic effect of hierarchical porosity and hybrid dielectric fillers, the optimized film achieves an ultrahigh solar reflectance of ∼97.2 % and a mid-infrared emissivity of ∼0.94, corresponding to a theoretical cooling power of ∼88.1 W/m 2 . Outdoor measurements demonstrate continuous subambient cooling, maintaining an average temperature ∼1.6 °C below ambient under realistic conditions. Building energy simulations across 18 representative cities predict substantial climate-dependent benefits, with annual cooling energy savings of up to ∼21.1 GJ per building and cooling-related carbon emission reductions of up to ∼6.3 t CO 2 -eq annually in high-cooling-demand regions. Combined with excellent UV resistance, hydrophobic self-cleaning capability, mechanical robustness, and chemical stability, this work provides a scalable and durable platform for long-term passive radiative cooling and sustainable thermal management.