Available in ½", ¾" and 1" thicknesses, our extruded polystyrene (XPS) insulation board offers our highest thermal performance in siding underlayment with R-Values of 3.0 (1/2") to 5.0 (1"). GreenGuard® CM Insulation Board is available as 2’ x 8’ and 4’ x 8’ (shown) sheets.