A smart window grows a silver shield to keep sunlight's heat out

November 2, 2026 report A smart window grows a silver shield to keep sunlight's heat out Andrew Zinin Author Lisa Lock Scientific Editor Robert Egan Senior Editor A window can admit welcome daylight but also let in unwanted heat, taxing air conditioning systems. Darkening the glass helps control glare, but the absorption of sunlight warms it. An ideal window would block more incoming heat while also letting trapped heat escape. To address this challenge, researchers at the Chinese Academy of Sciences, Northeast Forestry University and collaborating institutions have developed a colorful smart window with a reflective silver layer that activates when a voltage is applied. The layer turns a tinted, see-through pane opaque, providing shade and privacy. A separate outer coating helps the window release heat to the outside of the building. In outdoor tests, small structures covered by the prototype window stayed cooler than those covered by quartz glass or other commercial smart windows. The study, published in Nano Letters reveals a technology that manages daylight, privacy and heat at the same time. A tunable silver layer The design accomplishes two complementary functions: reflecting incoming sunlight and shedding heat through infrared radiation. Even in its transparent state, the window's ultrathin layers reflect a substantial share of near-infrared sunlight, which adds heat without providing visible illumination. A silicone coating on the outside of the glass allows heat at longer infrared wavelengths to escape into the atmosphere. For privacy, the application of a small voltage deposits silver from a gel onto an internal surface. This temporary layer increases sunlight reflection and makes the pane opaque. Reversing the voltage removes the deposited silver, restoring transparency. In one tested design, average visible-light transmission fell from about 44% to below 5%. Near-infrared reflection rose from roughly 54% to 83%. The heat-emitting coating continued working in both states. The layered structure also gives the window its color. Light waves reinforce or cancel one another as they interact with the thin layers, favoring some colors over others. Changing layer thicknesses during fabrication produced samples with tints including light yellow, pale cyan, gray-purple and rose red. Switching the silver layer also changed the reflected appearance. This adaptability offers designers a choice of colors, although it does not mean a single pane can display any color on command. Testing the window in the sun The researchers tested the design outdoors in Shanghai by covering small enclosures with different window samples and measuring the air temperature inside. In one comparison, the prototype's enclosure averaged about 3.4°C cooler during daylight than the enclosure covered in quartz glass. The largest difference reached approximately 7°C. Switching from transparent to opaque strengthened the cooling effect. A separate model-house experiment under simulated sunlight demonstrated that adjustment. Compared with quartz glass, the prototype kept the interior an average of about 4.3°C cooler in its transparent state and 5.9°C cooler when opaque. These measurements show cooling only in small experimental setups, however, rather than occupied buildings. Switching tests also found little change in measured reflectance after 350 cycles, but of course years of outdoor service remain unproven. The direction the window faces matters, too. The researchers describe the heat-emitting feature as "designed for sky-facing windows." Vertical panes would need a modified surface to direct more outgoing heat toward the sky. Skylights therefore offer a natural starting point for commercial applications: They admit daylight where strong sunshine can also cause overheating. An electrically controlled silver layer could let the same pane provide daylight when wanted, stronger shading when needed and a surface that sheds heat outward. Written for you by our author Andrew Zinin, edited by Lisa Lock, and fact-checked and reviewed by Robert Egan—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive. If this reporting matters to you, please consider a donation (especially monthly). You'll get an ad-free account as a thank-you. Publication details Jingjing Mao et al., Adaptive and Multicolored Electrochromic Smart Window with Transparent–Opaque Switchable Radiative Cooling, Nano Letters (2026). DOI: 10.1021/acs.nanolett.6c03931 Journal information: Nano Letters © 2026 Science X Network