The film is about as thick as kitchen aluminum foil, slightly thicker, in fact. A layer of silver lies beneath it. That was all the researchers at the University of Colorado Boulder needed in 2017 to create a material that will cool any roof, or any surface covered by it, including when exposed to full sun rays, using no power or water. According to CU Boulder's announcement of the research, even 10 to 20 square meters of such film covering your roof can noticeably cool a whole family-size home in summertime.
The material is simpler than it may first appear
The researchers used minute glass spheres, measured in micrometers, and randomly distributed them throughout a polymer film. These tiny glass spheres scatter sunlight that falls on them, preventing the surface beneath from absorbing the light. Beneath the film is a silver layer that reflects any sunlight that passes through the glass layer. The resulting film is about 50 micrometers thick, roughly comparable to kitchen aluminum foil. That matters operationally because the film can be manufactured on rolls, much like cling film.
Why sunlight usually wins, and how this film beats it
All surfaces on Earth radiate heat as infrared energy, and some of that energy escapes into outer space. But during daytime, the incoming energy from the sun overpowers the natural tendency to radiate. The CU Boulder coating addresses both problems at once. It reflects almost all incoming solar energy while still allowing the surface to radiate heat upward into space. The peer-reviewed study, titled "Scalable-manufactured randomized glass-polymer hybrid metamaterial for daytime radiative cooling," published in Science and indexed in PubMed, reported a cooling capacity of 93 watts per square meter at noon under full sun.
