TPO and PVC roofs are the most popular in the Thermoplastic Category. These single-ply membranes are composed of polymers, which soften when heated and harden when cooled. This process is repetitive provided the material is not heated above the point at which decomposition occurs. These membranes can usually be hot air welded throughout their service life. When maintained, TPO (Thermoplastic Olefin) has a typical lifespan of 15-25 years and PVC (Polyvinyl Chloride) has a lifespan of 15-20 years.