The new film works by a process called radiative cooling. This takes advantage of that fact that Earth’s atmosphere allows certain wavelengths of heat-carrying infrared radiation to escape into space unimpeded. Convert unwanted heat into infrared of the correct wavelength, then, and you can dump it into the cosmos with no come back.
…their film, placed atop an average American house, would be enough to keep the internal temperature at 20°C on a day when it was 37°C outside. [17° difference]