Glass Glossary

Airspace Width


Last Updated: January 8, 2024

Airspace width, also referred to as gap width, is the distance between the two panes of glass within an Insulating Glass (IG) unit. It plays a crucial role in the thermal performance and overall efficiency of an IG unit. The airspace is typically filled with air or an inert gas like argon to improve the insulation properties of the unit. 

Airspace Width Can Affect U-Factor

The airspace width directly influences the U-factor of the IG unit. Wider airspaces can enhance the U-factor by augmenting resistance to heat transfer between the glass panes, but only up to a certain limit. If the airspace is excessively wide, convection currents within the gas can intensify heat transfer, counteracting the advantages of a broader gap. For North American wintertime conditions, as specified by NFRC (0° F), the optimal airspace is approximately 1/2″. In Europe, under wintertime conditions (0° C or 32° F), the optimal airspace is slightly broader, roughly 3/4″, because milder winter temperatures result in reduced convection.

Argon gas is commonly chosen to fill the airspace in IG units due to its low thermal conductivity and cost-effectiveness relative to other gases. Using argon gas, the benefits to the U-factor are most pronounced with an airspace of about 1/2 inch (13mm). Beyond this measurement, the performance enhancements tend to wane due to convection.

In addition to thermal performance, the airspace width also affects other properties of the IG unit, such as sound insulation and the overall thickness of the unit. When selecting IG, it is essential to consider the appropriate airspace width to achieve the desired balance of thermal performance, noise reduction, and overall unit size.