The glass panes in insulating glass, 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 earlier spacers were made primarily of steel and aluminium, and their lower price means that they remain common.
However, because metal-based spacers conduct heat (unless the metal is thermally enhanced), this can inhibit the ability of the insulating glass unit to do what it is supposed to, i.e. reduce heat flow. 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 aluminium that also contains a highly structural thermal barrier reduces condensation on the glass surface and improves insulation, as measured by the overall U-value.
