Maintaining cool indoor environments in warm climates currently relies predominantly on power-intensive HVAC systems to transfer heat from inside and expels it outside, contributing to both greenhouse gas emissions and the local outdoor temperature (heat-island effect). ChillSkyn proposes a universal, electricity-free cooling solution leveraging the coldness of outer space. This is enabled through the application of a nano/microporous passive daytime radiative cooling polymer that effectively reflects the sun’s radiation while strongly emitting in the atmosphere’s transparent infrared window. ChillSkyn’s cooling solution is retrofittable to various outdoor surfaces, enabling a reduction in ambient temperature during daytime.