a search turned up this previous post:
RE: TPO versus EPDM
No. I don't know what the TPO type is. I'm sure that it has a fabric backing though. In simple terms TPO is vinyl, EPDM is rubber. About 10 yrs ago Jayco for a period of time was using felt backed TPO on some models until it was later discovered that the felt was wicking in and retaining moisture. I know of no TPO membrane used today that has felt backing and given the choice would prefer TPO over EPDM. Our current Coachmen has an EPDM roof and as is typical has the odd wrinkle, our previous K-Z Spree had a TPO roof which was perfectly flat & even throughout.
bumpy