Thermoplastic Polyolefin (TPO) is a type of single-ply membrane for roofing applications. Another type is Ethylene Propylene Diene Terpolymer (EPDM). A single-ply membrane is a sheet of roofing material that is mechanically attached, adhered, or ballasted to a building's insulation to create a layer of protection over a commercial structure. TPO membranes are made from a blend of polymers and rubbers, usually polypropylene, ethylene rubber, and reinforced special fabric.