This is a 25 mm Hydrophilic Pure Silver membrane filter with a 0.45 um ( 0.45 micron filter ) pore size. Used for air monitoring of carbon black, coal tar products, coke oven emissions & silica. R. Silver Membrane Filter, 0.45 µm, 25 mm MSDS (material safety data sheet) or SDS, CoA and CoQ, dossiers, brochures and other available documents.