Double glazing. Illustration of a section of insulated glazing, commonly known as double glazing. A double glazed window consists of two glass panes separated by a vacuum or space filled with air, or an inert gas such as argon (yellow spheres). A vacuum, air and argon are poor conductors of heat, and form an insulating layer. The panes are held apart by spacers (yellow strips), often containing a desiccant to prevent condensation. Significantly less heat is lost through double glazing than through a single-glazed window.