Whatman 7060-1304 Polycarbonate Cyclopore Track-Etched Membrane Filter, 13mm Diameter, 0.4 Micron (Pack of 100) Cyclopore polycarbonate (PC) membrane Circle; 0.4m; 13mm Smooth flat membrane ensures particles are retained on the surface so that they are easily visible under a microscope Membranes are produced from a pure polymeric film and give exceptional chemical cleanliness True surface capture provides easy examination of samples and short analysis times