What is XPS? There are many types of plastic foam insulation material available today and extruded polystyrene foam insulation (XPS) is one of the best for both general and specialized applications. Its excellent resistance to moisture, imperviousness to rot, mildew and corrosion, controlled compressive strength and ability to maintain insulating power make XPS foam a premiere insulating material for commercial, industrial and residential structures, as well as for critical civil engineering uses The closed-cell structure and lack of voids in XPS helps the foam to resist moisture penetration better than other types of insulating materials. In fact, when it comes to resisting water moisture absorption, there is not another insulation product that can perform as well without the use of a facer or laminate