Styrofoam™ Brand Tongue and Groove Extruded Polystyrene Foam Insulation (XPS) features tongue and groove edges on all four sides of 2’ x 8’ boards 1” thick or less and on the long edges of all other boards. The lightweight, moisture-resistant and thermally efficient Type IV extruded polystyrene foam insulation is suited for a wide range of residential and commercial construction applications.