An insulated glass unit (commonly IGU) is made of two or three panes of float glass distanced 8 to 16 mm from each other. The gaps between the panes are filled with air, argon or krypton and hermetically sealed.

This technology provides a vast improvement in thermal insulation over single glazing. The U-value of a single 4 mm glass pane, for example, is 5.8 W/m²K, whereas a standard triple glazed unit is 0.7 W/m²K. This, of course, provides considerable savings potential by way of a discerning window choice.

IGUs also offer excellent sound insulation which can be boosted and fine-tuned using
accoutic interlayers, differing glass thicknesses and edge seals.