To help protect against ozone and UV rays, EPDM roofing membrane is designed to oxidize or shed over time. This is not a concern, though, because it probably will shed less than 10 percent of its overall thickness in a 10- to 12-year time period.
TPO is yet developing its track record with expectations of a 20 year time period.
As a result of the shedding, the tell-tale signs of EPDM rubber are the gray or white streaks that you see on the sides of the RV.
TPO roofing does not oxidize or shed, so there are no gray or white streaks. Another way to distinguish between the two is to see how slippery the rubber surface is when it is wet. EPDM roofing is extremely slippery when it is wet, whereas TPO is not.