Abstract: Plastic foils containing nonabsorbing pigments can display a high reflectance of solar radiation combined with a high transmittance in the atmospheric window region in the thermal infrared. Such foils can be applied as selective covers enabling radiative cooling of an underlying material during the night and avoiding heating in direct sunlight during the day. The foils could be used for condensing water or cooling food, buildings, etc. We have prepared ZnS pigmented polyethylene foils with various thicknesses and volume fractions of pigments. The optical properties of the foils were compared with theory, and good agreement was achieved for pigment volume fractions up to 0.1. The optimum solar reflectance of the foil is 0.825 for the available pigment powder; but should be 0.88 if heating were to be avoided at noon with the sun in its zenith. The cooling power for a radiator covered with the best sample is 52 Wm$+$MIN@2$/ at night, and the equilibrium temperature of a radiator is 12 K below the ambient temperature. Heating of the radiator is avoided 18 hours per day, and the radiator temperature at noon is 8 K above the ambience. !39
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