An insulating glass unit (UVA), also called multiple glazing or chamber glazing, is a glazing formed by two or more sheets of glass without direct contact between them, arranged in parallel and forming a single unit.

The intermediate space between the glasses is usually filled with dehydrated air or another inert gas, but it is also possible to form a vacuum, thus improving its performance. In any case, the chambers are closed hermetically to prevent air circulation and the entry of contaminants. The thermal resistance of the glass unit can be increased by placing low emissive layers, by introducing metallic deposits on the inner face of the chamber in the interior glass. At the beginning of the century, this type of glazing has displaced monolithic glazing in developed countries in a large part of buildings (mainly in cold climatic zones), thanks to its insulating properties.

The thickness and type of glass depend on the size of the unit and the anticipated wind exposure. It is also a function of the requirements for solar control, acoustic insulation and safety and security specifications.

The total thickness of the insulating glass units most used in construction varies, depending on their dimensions, between 12 and 25 mm. When the size of the cloth is important, it can reach thicknesses of up to 35 mm. The mass of a UVA can vary between 15 and 60 kg/m², depending mainly on the total thickness of glass used.

Thermal transmittances for the simplest double glazing can vary between 3.30 W/m².K and 2.90 W/m².K, where a lower value means better insulation. Among the factors that influence transmittance are the quality of the sealing system, the replacement of air by argon, the separation between glasses and the level of thermal emissivity of the glass. In the event that one or two of the glasses are low emissivity (LowE), the thermal transmittance can be between 2.50 and 1.70 W/m².K.[1]​.

If a higher level of insulation is needed, triple glazing can be used with low-emissive glass, which can obtain thermal transmittance values ​​close to 0.8 W/m².K.

To form the intermediate chamber, each insulating glass unit contains an aluminum frame filled with zeolite molecular sieve or silica gel (both dehydrators), although similar dehydrating structures can also be composed that glue the two glasses together. This frame is then usually fixed with some type of butyl and sealed with silicone, polysulfide or polyurethane. This chamber can also be filled with some noble gas, usually argon or krypton, thus improving the thermal insulation properties. In Germany, vacuum chamber glazing (a few millimeters thick) has been developed. With this solution it is expected that there will be no heat transfer by convection or conduction.