Regular Price $352.37 Price $306.00. Add to Cart. Whatman Nuclepore Track-Etched Polycarbonate AOX Membrane, 0.4 µm Pore Size, 25 mm Circle, 100 Pack, 110637 (DISCONTINUED) Regular Price $539.04 Price $468.73. Whatman Nuclepore Polycarbonate Black Membrane Filter, 0.2 µm Pore Size, 25 mm Circle, 100 Pack, 110656.