Double-glazed units consist of two glass panes that are separated by a sealed space, typically filled with air or an inert gas like argon. The use of two glass panes provides added insulation and creates a barrier against heat transfer, noise, and other external factors.

The sealed space between the glass panes in this type of glazing acts as an insulating air gap. This gap helps to reduce heat transfer, minimizing heat loss during colder months and heat gain during warmer months. The air or gas within the gap provides additional insulation, enhancing energy efficiency and thermal comfort.

Many double-glazed windows feature a Low-E (low-emissivity) coating on one or both of the glass panes. This coating helps to reflect heat into the room while allowing natural light to pass through. It improves the thermal performance of the windows, reducing heat loss and enhancing energy efficiency.

The two glass panes in double glazing are separated and supported by a spacer bar. The spacer bar is typically made of a low-conductive material, such as aluminium or warm-edge composite, which helps to maintain the integrity of the sealed space and prevent heat loss through the edges of the windows.

In some cases, the sealed space between the glass panes is filled with an inert gas, such as argon or krypton. These gases are denser than air and provide better insulation properties, further improving the energy efficiency and thermal performance of the double glazing.