Improved window energy efficiency with thermal insulating polymer-air multilayer

Highlights: • A cost-efficient polymer-air multilayer coating was developed to enhance the window energy efficiency. • It was more thermal insulating than many silica aerogels, and equipped with a low-e layer. • The U-factor could be reduced by ~50%, by a 6-mm-thick coating. • The coating was highly transparent, low-haze, and structurally robust and resilient. Polymer-air multilayer (PAM) was developed to reduce the heat loss through windowpane. A PAM consists of a few polymer films separated from each other by air gaps. Thanks to the excellent optical properties of the polymer films, the visible transmittance of PAM is higher than 70%, and the haze is ~1.8%. PAM not only has mechanisms to reduce the conductive and convective heat transfer, but also can obstruct the radiative heat transfer. By mounting a 6 mm-thick 4-layer PAM on the indoor side of a glass pane, the overall U-factor is lowered from 5.8 W/(m²·K) to 2.85 W/(m²·K)$.$ PAM is resilient and robust, attractive for the window retrofitting applications.