Abstract: A spacer for separating panes of glass in a sealed window unit is formed of a thermosetting resin reinforced longitudinally with continuously extending glass fibres. A layer of a foil material is introduced into the part during the pultrusion process so that the foil is embedded within the part and defines a moisture impermeable layer in the outer wall of the part. The foil can be carried into the part on a layer of paper or polyester which combines with the resin in a bonding action.