PTFE Membrane Filters. Biopore Membrane Filter roll, Hydrophilic PTFE This Biopore membrane roll is hydrophilic, with a pore size of 0.4 microns. 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.