Insulating glass units, or IGUs, are designed to keep homes warmer in the winter and cooler in the summer.

An insulating glass unit commonly consists of two (sometimes more) panes of glass separated by a spacer material and sealed together at the edge. The insulating airspace is filled with air or a noble gas, such as argon or krypton inside. Each glass pane has two surfaces, so typical double-paned IGUs have four surfaces.