27/2/2018 · A typical membrane cartridge will have anywhere between 6 ft 2 and 8 ft 2 of surface area per 10” filter length. Assuming a media, such as polyethersulfone (PES), is 70% porous, the filter then has about 6 – 8 trillion pores, all of which must be filled with liquid in order to conduct a valid integrity test and obtain a passing integrity test value.