Thermoplastic materials are distinguished from thermoset materials in that there is no chemical crosslinking. Thermoplastic membranes can be repeatedly softened by heating or hardened when cooled. Because of their chemical nature, thermoplastic membranes are typically seamed by heat welding with hot air or solvent welding.

These are the common subcategories of thermoplastic roof membranes:

  • Polyvinyl Chloride (PVC)
  • PVC Alloys or Compounded Thermoplastics
  • Copolymer Alloy (CPA)
  • Ethylene Interpolymer (EIP)
  • Nitrile Alloys (NBP)
  • Tripolymer Alloy (TPA)
  • Thermoplastic Olefin (TPO)
  • Chlorinated Polyethylene (CPE)

The most common thermoplastic roof membranes are PVC and TPO. These roof membranes can be installed fully adhered, mechanically attached or ballasted. Most PVC and TPO membranes do not receive surfacings. The following provides general descriptions of these two systems.

Polyvinyl Chloride (PVC)

PVC sheets are produced by calendaring, spread coating or extruding, and typically are reinforced with polyester or glass-fiber mats or scrim. PVC sheets contain plasticizers and stabilizers, as well as other additives to impart flexibility and achieve other desired physical properties. Some membranes are available with nonwoven fleece backing adhered to the underside of a sheet.

  • Sheet widths range from 6 feet to 12 feet wide
  • Sheets are typically 45 mils to 90 mils thick
  • Seams are sealed by heat or chemical welding
  • PVC membranes are produced in numerous colors, though gray and white are the most common

Thermoplastic Olefin (TPO)

TPO membranes are produced by calendering with lamination, extrusion with lamination, or extrusion-coating techniques. TPO sheets are a blend of polypropylene and ethylene propylene polymers and usually are reinforced with polyester. TPO sheets contain colorant, flame retardants, UV absorbers and other proprietary substances to achieve desired physical properties.

  • Sheet widths range from 6 feet to 12 feet wide
  • Sheets are typically 40 mils to 100 mils thick
  • Seams are sealed by heat welded with hot air
  • TPO membranes commonly are white