The most common application of passive daytime radiative cooling currently is on building envelopes, including PDRC cool roofs, which can significantly lower indoor space temperatures within buildings. A PDRC roof application can double the energy savings of a white roof. This makes PDRCs a sustainable and low-cost alternative or supplement to air conditioning by decreasing energy demand, alleviating energy grids in peak periods, and reducing CO 2 emissions caused by air conditioning's release of hydrofluorocarbons into the atmosphere which can be thousands of times more potent that CO 2.