XPS, or extruded polystyrene, is a high quality insulating material that retains its properties even under very harsh conditions.
It is made of expanded polystyrene by extrusion through a slot die. The resulting polystyrene has a closed-cell structure and a smooth surface, due to which it has greater mechanical strength. It is also harder and less absorbent.
Due to its properties, it is often used for the insulation of basement walls and foundations. They are also used, among others, for the insulation of ceilings and inverted roofs, terraces etc.