TPO, or Thermoplastic Polyolefin, and PVC, or Polyvinyl Chloride, are both made up of a synthetic substance specifically designed to soften when heated and harden when cooled. TPO roofing is a single-ply system normally installed using one of three distinct methods. PVC roofing offers a wide selection of choices including panels that can be attached in additional ways. Both systems use heat to seal the seams between the panels or sheets and offer excellent waterproofing and protection from abusive conditions.