Abstract
[...]they can radiate away enough heat to consistently stay a few degrees cooler than surrounding air; research suggests that temperature differences could exceed 10 °C in hot, dry places2,3. To create something highly reflective, the researchers alternated four thin layers of materials that refract light strongly (hafnium dioxide) and weakly (silicon dioxide, or glass), a commonly used motif in optical engineering that works because of how light waves interfere as they pass through different layers. Many polymers naturally emit in the infrared 8-13-pm range because their chemical bonds, such as those between carbon atoms or between carbon and fluorine, eject packets of infrared light when they stretch and relax, explains team member Yuan Yang. Just like polymers, wood contains chemical bonds that emit the right kind of infrared radiation, says Li.