Insulated glazing (IG), is double, triple or more glass window panes separated by a vacuum or other gas filled space to reduce heat transfer.
Insulated glass units are manufactured with glass in range of thickness from 3 mm to 10 mm (1/8″ to 3/8″) or more in special applications.
The glass panes are separated by a “spacer”. A spacer is the piece that separates the two panes of glass in an insulating glass system, and seals the gas space between them. The maximum insulating efficiency of a standard IGU is determined by the thickness of the space. Typically, most sealed units achieve maximum insulating values using a space of 16–19 mm (0.63–0.75 in) when measured at the centre of the IGU. IGU thickness is a compromise between maximizing insulating value and the ability of the framing system used to carry the unit.