The glass panes are separated by a “spacer”. A spacer, which may be of the warm edge type, is the piece that separates the two panes of glass in an insulating glass system, and seals the gas space between them. The first spacers were made primarily of steel and aluminum, which manufacturers thought provided more durability, and their lower price means that they remain common.
However, metal spacers conduct heat (unless the metal is thermally improved), undermining the ability of the insulated glass unit (IGU) to reduce heat flow. It may also result in water or ice forming at the bottom of the sealed unit because of the sharp temperature difference between the window and surrounding air. To reduce heat transfer through the spacer and increase overall thermal performance, manufacturers may make the spacer out of a less-conductive material such as structural foam. A spacer made of aluminum that also contains a highly structural thermal barrier reduces condensation on the glass surface and improves insulation, as measured by the overall U-value.
- A spacer that reduces heat flow in glazing configurations may also have characteristics for sound dampening where external noise is an issue.
- Typically, spacers are filled with or contain desiccant to remove moisture trapped in the gas space during manufacturing, thereby lowering the dew point of the gas in that space, and preventing condensation from forming on surface #2 when the outside glass pane temperature falls.
- New technology has emerged to combat the heat loss from traditional spacer bars, including improvements to the structural performance and long-term-durability of improved metal (aluminum with a thermal barrier) and foam spacers.