in order to make weather seals from closed cell elastomer foam material , molten plastic is extruded over a substrate of the foam material . surface reactions during extrusion are avoided by continuously pulling the substrate through an oven chamber to degas the material at least on its outside to a limiting thickness of the order of 10 - 30 mil to form a skin or crust . the extrusion of the over - coating is carried out to form a sleeve while the substrate is still hot . since the skin is a degassed region on the outside of the foam substrate , reactions which may cause blistering and prevent the extrusion of a smooth and firmly adhering skin are avoided . the substrate material is preferably a thermosetting epdm rubber closed cell foam , and the over coating material is a thermoplastic elastomer .