Although there is no true standard of nomenclature for blended polymers, TPO typically stands for a category of polymers known as Thermoplastic Polyolefins. Polyolefins are a group of polymers comprised of mainly hydrogen and carbon, mainly polyethylene and polypropylene. TPO's are typically a blend of polyolefins with other additives designed to create a polymer which has a very specific processing and performance characteristic. In many cases the TPO blend has less semi-crystallinity, less strength, more.
If you have questions about the installation of these various systems, check the videos on gaf.com or call your local GAF sales representative. Related articles: PVC vs. TPO: Is the Debate Over? KEE: What are the Pros and Cons? How to Clean a TPO or PVC Roof Cool Weather Application Instructions for TPO and PVC.