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

Energy-saving cooling materials with strong operability are desirable towards sustainable thermal management. Inspired by the cooperative thermo-optical effect in fur of polar bear, we develop a flexible, superhydrophobic and reusable cooling "skin" by laminating a polydimethylsiloxane film with a highly-scattering polyethylene aerogel. Owing to its high porosity (97.9%) and tailored pore size of 3.8 ± 1.4 μm, superior solar reflectance (R ̅_sun ~0.96) and high transparency to irradiated thermal energy (τ ̅_(PE,MIR) ~0.8) can be achieved 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 °C in a metropolitan environment, with an estimated limit of 14 °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 to more cost-effective and scalable cooling materials.