DuPont™ Styrofoam™ Brand Deckmate™ Plus Tapered Extruded Polystyrene (XPS) Foam Insulation is an extruded polystyrene foam featuring smooth, high-density skins and a closed cellular structure. Designed with a positive slope for drainage, it has a higher compressive strength than other commonly used foam plastic insulations in order to provide additional membrane support for conventional low-slope roof applications.