Polymer solar filter for enabling direct daytime radiative cooling

Passive radiative daytime cooling is a low-cost solution to improve human comfort and reduce the energy demands of cooling on a global scale. We present the first demonstration of direct full-sun daytime radiative cooling using an all-polymer filter that blocks solar irradiance while maintaining high transmittance in the long-wave infrared (LWIR). Warm objects and surfaces radiatively transfer heat through the polymer solar filter to the cold sink of space, decreasing temperatures up to 10 degrees C during day and night. The polyethylene (PE) filter exploits scattering by size-controlled air pores to maximize reflection of solar photons, while preserving the LWIR transparency inherent to PE. We demonstrated cooling power of over 110 W/m(2) for an emissive surface placed beneath the solar filter. Scalable, low-cost manufacturing of a radiative cooling polymer solar filter allows direct full-sun daytime cooling of heat-emitting surfaces in a variety of settings.