Open-Cell XPS Foam 20 mm (Green Stuff World)Open cell extruded polystyrene XPS 20 mm Open cell XPS extruded polystyrene foam, also called Styrofoam, is a lightweight, strong, durable, and less dense material than its sister closed cell XPS foam in blue, giving it a "low memory" effect that is ideal for marking, engraving, texture transfer, scratching, and roughing. Open Cell XPS Foam can be used to create various scenery such as hills and cliffs, game boards, different model building elements