  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 and reusable cooling skin
via laminating a polydimethylsiloxane film with a highly-scattering
polyethylene aerogel. Owing to its high porosity of 97.9% and tailored pore
size of 3.8 +- 1.4 micrometers, superior solar reflectance of 0.96 and high
transparency to irradiated thermal energy of 0.8 can be achieved at a thickness
of 2.7 mm. Combined with low thermal conductivity of 0.032 W/m/K of the
aerogel, the cooling skin exerts midday sub-ambient temperature drops of 5-6
degrees in a metropolitan environment, with an estimated limit of 14 degrees
under ideal service conditions. We envision that this generalized bilayer
approach will construct a bridge from night-time to daytime radiative cooling
and pave the way for economical, scalable, flexible and reusable cooling
materials.
