The Latest Update of PTFE Membrane Filter. Free sample unlaminated PTFE membrane filter online. Durapore® Membrane Filter, 0.22 µm | Sigma-Aldrich Gravimetric Analysis Membrane Filter, 0.22 µm, mixed cellulose esters with thin pad, 37 mm, white. A 0.22 µm pore size non-sterile filter validated for air monitoring.