Polyethersulfone (PES) Membrane Filters, 0.45 Micron, 13mm, 100/Pk. Sterlitech PES (polyethersulfone) membrane filters, 0.45 micron pore size, 13 mm diameter, pack of 100. Hydrophilic, low protein/drug binding, minimal extractables, and broad chemical tolerance; ideal for pharmaceutical, medical, and life science applications.