IPS 83440 Gray 40-mil Membrane, 4-Feet x 50-Feet Pvc shower pan Liner 40 mil. Membrane Meets ASTM d-4551 No underlay mount required - may be glued directly to drain to positive seal Meets fha & hud requirements for shower pan Liner 40 mil Thick Meets ASTM D-4551 No underlay mount required - may be glued directly to drain to positive seal Meets FHA & HUD requirements for shower Pan Liner