TPO (thermoplastic polyolefin) single-ply roofing is a plastic membrane typically 0.45 to 1.5 mm thick that is heat-welded to adjacent panels to create a continuous waterproof surface. This system is widely used on flat and low-slope commercial and industrial buildings. TPO combines the durability of plastic with good flexibility and UV resistance. The membrane is white or light-colored, reflecting solar heat and reducing cooling costs. Installation begins with preparation of the roof deck, which must be smooth and clean to prevent puncture of the membrane. A cover board (wood fiber board or foam) may be installed under the TPO to provide a smooth surface and additional insulation. The TPO membrane is laid out in panels, typically 6 to 10 feet wide, and is attached to the deck. Attachment may be fully adhered (glued), mechanically fastened, or ballasted (weighed down with gravel or pavers). Fully adhered systems provide superior wind resistance. Mechanical fastening is less expensive but requires sealing around fasteners. Ballasted systems allow membrane re-use when re-roofing. Adjacent panels are heat-welded together with a hot-air welding gun. The welder creates a thermal bond between panel edges that is as strong as the membrane material itself. Proper welding technique is critical; under-welded or over-welded seams fail. Field penetrations are sealed with TPO flashing cut and heat-welded in place. Roof projections including curbs, chimneys, and vents require flashing integration. TPO roofs last 20 to 30 years with proper installation and maintenance.