Double-pane windows, which sandwich a layer of insulating air, can offer improved energy efficiency over single-pane windows, but replacing existing single-pane windows can be expensive or technically challenging. A more economical but less effective option is to coat single-pane windows with translucent metallic films capable of absorbing some solar heat in winter without compromising clarity of the glass. To improve the coating’s efficacy, researchers say that nanoscale technology may help elevate thermal performance to that of double-pane windows in winter.