Window Retrofit Applique using Phonon engineering (WRAP) | SRI International

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Window Retrofit Applique using Phonon engineering (WRAP)

SRI is developing a new film to reduce heat loss through single-pane windows.

A substantial number of U.S. buildings have single-pane windows that lose much more heat than double-pane or other advanced units, but replacing single-pane windows can be cost-prohibitive. SRI is working with partner organizations to develop a new type of film that can be used to easily retrofit single-pane windows to make them more efficient without blocking visible light.

“Unparalleled” thermal insulation

SRI and its partners are developing a new “phononic metamaterial” that is expected to be an unparalleled thermal insulator for single-pane windows. The film is based on an entirely new approach to thermal barriers that uses nanoparticles to reflect heat and provide superior thermal insulation.

The transparent, adhesive product can be applied directly onto existing windows to improve window energy efficiency and impart other important qualities without substantially affecting window appearance. For example, the coating allows light to transmit through the window and brighten the interior. The film will also reduce condensation and possibly make the window more soundproof, which will improve occupant comfort. Ultimately, researchers expect the technology will enable development of other nonporous insulating materials as well.


If successful, SRI’s innovations could enable energy-efficient retrofits for the substantial remaining stock of single-pane windows in the United States. Retrofitting, rather than replacing, single-pane windows could reduce heat loss and save roughly the amount of electricity needed to power 32 million U.S. homes each year.

Consumers will benefit from more efficient heating, reduced window condensation in cold weather, and better soundproofing. Applying SRI’s novel film to windows will afford significant economic benefits to homeowners and businesses, and using less electricity, natural gas, and/or heating oil to warm buildings will reduce greenhouse emissions associated with these energy sources.

The information, data, or work presented herein was funded in part by the Advanced Research Projects Agency-Energy (ARPA-E), U.S. Department of Energy, under Award Number DE-AR0000735. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.