Insulating glass – also known as an insulating glass unit (IGU) – consists of at least two panes of glass held apart by an edge spacer. The cavity between the panes is filled with dry air or a noble gas such as argon or krypton, which improves thermal insulation. A desiccant inside the spacer absorbs moisture so the panes do not fog up from the inside.
The insulating effect works because the gas in the cavity conducts heat far less than a single pane. In addition, invisible metal coatings (low-E or thermal coatings) help keep heat inside the room. How well a glazing insulates is expressed by the Ug value: the lower, the better. Modern triple glazing reaches considerably lower values than older double glazing.
You need insulating glass wherever living comfort, heating costs and sound protection matter – in new builds, window renovations, conservatories, or when replacing fogged-up, leaky old windows. In Switzerland, good glazing is also often a condition for subsidies and for meeting cantonal energy regulations.
Pay attention to the Ug value of the glass and the U value of the whole window, to an intact edge seal (a "warm edge" instead of aluminium) and to a specialist firm that installs it correctly. A common mistake is to look only at the glass while neglecting the frame and proper installation. Condensation between the panes is a sign of a failed edge seal.