Summer cooling costs are going up. Roofs that soak up heat only make things worse. Researchers at City University of Hong Kong, working with a team at Hong Kong Polytechnic University, have developed a tile that reflects 99.6% of sunlight. This is an exceptionally high reflectivity for a passive material. The results were published in the peer-reviewed journal Science in November 2023, in a paper titled "Hierarchically structured passive radiative cooling ceramic with high solar reflectivity." Professor Edwin Chi-Yan Tso and PhD student Kaixin Lin led the work. This is not a paint or a coating you can apply. It's a tile built from the ground up at the microscopic level, designed to bounce nearly all sunlight back into the sky instead of letting it heat buildings.
Why an insect inspired this cooling material
The design gets ideas from the Cyphochilus beetle, which has some of the most reflective surfaces in the world. The beetle's scales have a random pattern of very small parts that spread light in every direction instead of absorbing it. The CityU group achieved this result using alumina, a common ceramic, by shaping it into a spongy structure that scatters almost all sunlight. The material reflects 99.6% of light. It also releases heat very well in the middle of the infrared range, with a heat release of 96.5%, according to the CityU research notice. The tile reflects most of the heat that comes in and sheds the small amount it absorbs, preventing heat from building up.
