A method of integrity testing porous materials that is non-destructive to the material being tested. The method includes humidifying the inlet gas stream to minimize or prevent the porous material from drying out. The inlet gas stream includes at least two gases, wherein one of the gases has a different permeability in liquid than the other, such as oxygen and nitrogen. The permeate gas stream may be subjected to a driving force such as reduced pressure to increase the flow of gases and reduce test time. Multiple porous materials can be integrity tested at the same time, such as by manifolding a plurality of them together. The integrity test is capable of detecting the presence of oversized pores or defects that can compromise the retention capability of the porous material.