The manufacturing process differentiates extruded polystyrene (XPS) from expanded polystyrene (EPS), which we discussed on the previous page. XPS starts as a molten material that's pressed into sheets. It's usually used as foam board insulation, although it can be used for general or specialized applications. XPS is resistant to moisture, rot, mildew and corrosion. Facers or laminate aren't required for it to adequately resist water absorption. The Extruded Polystyrene Foam Association reports that when XPS is used in a house for 15 to 50 years, it has net positive energy conservation and air emission benefits (during this time more energy is saved than consumed by manufacturing the insulation).