Colorful paints could keep buildings cool

About 15% of household electricity in the US goes to keeping buildings cool. Materials that reflect heat to passively cool buildings could save some of that energy. Yuan Yang, a materials scientist at Columbia University, wanted to make an inexpensive and practical coating to do that efficiently. Two years ago, his group developed a paintable, snow-white polymer with randomly shaped pores that are the right size to reflect visible and infrared light (Science 2018, DOI: 10.1126/science.aat9513). Half the energy in sunlight is in the infrared part of the spectrum, so a material that reflects those wavelengths can keep things cool even if it still absorbs some visible light. The group has now added color, which should make the coatings more attractive to homeowners and vehicle makers. The team showed that a double-layer coating of the porous polymer and regular paint is still a highly effective passive cooler—and coating the polymer with dyes that absorb only specific wavelengths is even more effective, as commercial paints typically absorb some infrared light. Their vividly colored coatings reduce surface temperatures by 5–10 °C in full sun (Sci. Adv. 2020, DOI: 10.1126/sciadv.aaz5413).