Engineers at the University of Colorado Boulder has developed a metamaterial – an engineered material not found in nature – which has the ability to cool objects even under direct sunlight with zero energy and water consumption.

A film of the metamaterial, when applied to a surface, cools the object underneath by efficiently reflecting incoming solar energy back into space while simultaneously allowing the surface to shed its own heat in the form of infrared thermal radiation.

The material takes advantage of passive radiative cooling, the process by which objects naturally shed heat in the form of infrared radiation.

Passive thermal radiative has been used for nighttime cooling but daytime cooling is more challenging as a even a small amount of directly-absorbed solar energy is enough to negate passive radiation. To overcome this, the researchers embedded visibly-scattering but infrared-radiant glass microspheres into a polymer film. They then added a thin silver coating underneath in order to achieve maximum spectral reflectance.

The glass-polymer hybrid material is slightly thicker than kitchen aluminum foil and can be manufactured economically on rolls, making it a potentially viable large-scale technology for both residential and commercial applications.

The researchers say that just 10 to 20 square metres of the material on a rooftop could keep a single-family house cool in summer and that there are potential uses in the power industry, aerospace and agriculture. One use could be for supplementary cooling for thermoelectric power plants, which currently require large amounts of water and electricity to maintain the operating temperatures of their machinery.