Low-Emissivity Glass

Low-emissivity glass, commonly called low-E glass, is architectural glass coated with a microscopically thin, virtually invisible metallic or metal-oxide layer that reflects long-wave infrared heat radiation while allowing visible light to pass through, reducing the amount of heat that escapes through a window in winter or enters in summer depending on which glass surface carries the coating. Developed from coating technologies of the 1970s and widely adopted from the 1980s and 1990s onward as energy codes tightened, it is now a standard component of most insulated glazing units in temperate and cold climates, and different coating formulations are tuned for either passive solar heat gain in cold climates or solar heat rejection in hot ones.