PTFE Membranes. Whatman PTFE PM2.5 Air Monitoring Membrane Filter, 2.0 µm, 46.2 mm, w/Support Ring, Sequentially Numbered, 50 Pack, 7592-104. Regular Price $557.06 Price $483.77. Add to Cart. Whatman 10411311, PTFE Membrane, TE Range (TE 36), 0.45 um pore size, 47 mm circle (50 pcs) Regular Price $312.65 Price $271.51. Add to Cart.