Milliseal Membrane Seal, PTFE, 18 mm. This is a 18 mm Hydrophobic PTFE Membrane Filter with a 0.45 micron pore size. For use in Sterilizing filtration, bioassays, solvent filtration. A 25 mm diameter sterile syringe filter with a 0.2 µm pore size hydrophobic PTFE membrane, ethylene oxide sterilized. Get Price.