Fisherbrand™ PTFE Filter Membranes. Fisherbrand™ PTFE membrane is hydrophobic filter made of polytetra-fluorethylene laminated with PP layer. Pricing and Availability. Sartorius™ Midisart™ 2000 PTFE Air Filter. Designed for easy handling and maximum safety in air filtration. Sartorius™ Midisart™ 2000 PTFE Air Filter entirely