Whatman® PTFE membrane filters TE 35 (circles), 0.2 μm, 50 mm. The 0.5 μm pore size is normally used. Air and gas sterilization make use of the hydrophobic characteristics of PTFE membranes and their ability to stop aqueous aerosols. Usual pore sizes are 0.2 μm and 0.5 μm. Sterile venting of vacuum manifolds, fermentation vessels, and