Double glazing is glass consisting of at least two panes of glass separated by a cavity with dehydrated air, arranged in parallel and forming a single glass unit
To form the air space, each insulating glass unit contains an aluminium frame filled with a dehydrating element. This frame is then normally secured with some type of butyl and sealed with polyurethane. This cavity can also be filled with some type of inert gas, usually argon or krypton, thus improving the thermal insulation properties.
Cross section of double glazing