Sterilizing Grade 0.2 Micron PTFE Membrane Filter Cartridge. SERENE Hydrophobic PTFE Sterilizing Grade 0.2um filter cartridges are highly retentive hydrophobic membrane designed for critical liquid and gas sterilization. Hydrophobic PTFE filter medium provides exceptionally high air flow rates at low differential pressures Naturally Hydrophobic Membrane also provides high assurance of filter integrity andlong life, during high temperature venting application and during repeated steaming.