I am trying to find the BET surface area of a polymer membrane, pore size of below 2 nm which is supported on top of a microporous support (I can choose any such as PES, PTFE, PVDF, Nylon or any other support). The polymer membrane is too thin so the weight is not enough for BET and as it is free standing so I can mount it on any support. My concern is that if I do BET of the composite membrane, polymer+support, the data will not be accurate as it will also include the surface area of support. Any suggestions please.