Scalable, Controlled Bimodal Pore-Structured Polymer Coating for Efficient Passive Daytime Radiative Cooling

Outdoor thermal irritation poses a serious threat to public health, with the frequent occurrence of increasingly intense heat waves. With the global goal of carbon peaking and carbon neutrality, there is an urgent need for a strategy that is efficient and can provide localized outdoor cooling without an intensive energy input. This paper demonstrated a rapidly formable polyurethane-based coating with controlled bimodal spherical micropores. Nano-Al2O3 particles (300 nm) embedded in the polymer were used for targeted enhancement of reflectance at 0.38–0.5 wavelengths. The enhanced film reflected 93% solar irradiance and selectively transmitted 95% thermal radiation (8–13 μm), enabling rapid cooling and the creation of a comfortable thermal microclimate to avoid overheating of 6–11 °C during daytime conditions. The ultrawide material compatibility and excellent adaptive mechanical strength of polyurethane-based coatings are expected to benefit the sustainable development of society in a wide range of fields, from health to economics.