Insulated Glazing Unit

An insulated glazing unit, often called an IGU or double or triple glazing, is a window assembly of two or more panes of glass separated by a sealed air- or gas-filled gap, most often held apart by a spacer bar around the edge, that reduces heat transfer through the window compared with a single pane. Commercial sealed double glazing dates to the early twentieth century and became widespread from the mid-twentieth century onward as energy costs and building codes made single-pane glazing increasingly impractical in temperate and cold climates, and the sealed gap is often filled with an inert gas such as argon to further reduce heat conduction. Combining an insulated glazing unit with a low-emissivity coating on one of its internal glass surfaces is now standard practice in most new construction in climates with meaningful heating or cooling loads.