Engineers at the Massachusetts Institute of Technology (MIT) have developed a heat-rejecting material in the form of a film that could be applied to cover the windows of a building to reflect up to 70% of the incoming sun's heat, thereby reducing energy consumption. The film can remain highly transparent below 32ºC. Above this temperature, say the researchers, the film acts as an "autonomous system" to reject heat. They estimate that if all exterior-facing windows in a building were covered by the film, the building's air conditioning and energy costs could be reduced by 10%.
This film is similar to clear plastic wrap, and its heat-rejecting properties come from tiny microparticles embedded in it. These microparticles are made of a type of phase-change material that shrinks when exposed to temperatures of 85 degrees Fahrenheit or higher. In their most compact configurations, the microparticles give the normally transparent film a more translucent or frosted appearance.
