Passive daytime radiative cooling enhances longwave infrared thermal radiation heat transfer on the Earth's surface through the infrared window with the coldness of outer space to achieve daytime cooling. Solar radiation is reflected by the PDRC surface to minimize heat gain and to maximize thermal emittance. PDRC differs from SRM because it increases radiative heat emission rather than merely reflecting the absorption of solar radiation. PDRC has been referred to as an alternative or "third approach" to geoengineering. PDRC has also been classified as a sustainable and renewable cooling technology.