Green-Manufactured and Recyclable Coatings for Subambient Daytime Radiative Cooling

Passive daytime radiative cooling, which reflects sunlight and simultaneously emits heat into space to cool surfaces without energy input, is a promising strategy for energy conservation. Integrating radiative cooling with building systems can tremendously alleviate electrical cooling, but manufacturing high-efficient and eco-friendly coatings remains an urgent and challenging task. Here, we present a simple and scale-up strategy for fabricating ultrawhite coatings consisting of porous ethyl cellulose matrix–random BaSO4 nanoparticles utilizing green solvents. With the synergistic effect of the ideal intrinsic properties of the materials and the strong Mie scattering of the porous structure, the ultrawhite coating possesses a record solar reflectance of 98.6% and a thermal emittance of 98.1%, resulting in a subambient temperature drop of over 2.5 °C under a solar intensity of ∼920 W m–2. Better yet, our coatings can be conveniently brushed, rolled, or sprayed onto various types of substrates, with excellent durability, self-cleaning, and cost-effectiveness, paving an attractive and viable pathway for large-scale applications in practical buildings.