Bioinspired "Skin" with Cooperative Thermo-Optical Effect for Daytime Radiative Cooling

Energy-saving cooling materials with strong operability are desirable for sustainable thermal management. Inspired by the cooperative thermo-optical effect in the fur of a polar bear, we develop a flexible, superhydrophobic, and reusable cooling "skin" by laminating a poly(dimethylsiloxane) film with a highly scattering polyethylene aerogel. Owing to its high porosity (97.9%) and tailored pore size of 3.8 +/- 1.4 mu m, it can achieve superior solar reflectance ((R) over bar (sun) similar to 0.96) and high transparency to irradiated thermal energy ((tau) over bar (PE,MIR) similar to 0.8) at a thickness of 2.7 mm. Combined with the low thermal conductivity (0.032 W m(-1) K-1) of the aerogel, the cooling skin exerts midday sub-ambient temperature drops of 5-6 degrees C in a metropolitan environment, with an estimated limit of 14 degrees C under ideal service conditions. Our generalized bilayer approach can be easily applied to different types of emitters, bridging the gap between night-time and daytime radiative cooling and paving the way for more cost-effective and scalable cooling materials.