A high-purity, thin PTFE membrane in a sequentially numbered chemically resistant polypropylene support ring for PM 2.5 ambient air monitoring. Whatman PM 2.5 membranes have low tare mass for accurate gravimetric determinations. The thermally stable design eliminates curling, keeps the membrane flat, and makes the filter robot-friendly. The PM 2.5 PTFE membranes are manufactured under clean room conditions. These chemically resistant, low chemical background filters permit sensitive, interference-free determinations. No glues or adhesives are used in making these products. PTFE filters are in conformance with the EPA PM 2.5 Reference Method. (Statement of Conformance is available prior to purchase and with purchase). Diameter: 46.2mm. 50/Pack. Whatman #: 7592-104.