|Understanding the Difference Between Membrane and Depth Filters
Membrane Filters — Membrane filters are made typically of MCE, PVC, copolymers, polycarbonate, silver, gelatin, or PTFE. They are precision cast into sheets, therefore, the pores are consistent and pore size ratings are more precise. During sampling, small particles pass through the pores in membrane filters leaving larger particles on the surface of the filter. A high amount of particles on the surface of a membrane filter can clog the pores causing particles that would normally pass through to be retained on the surface such as what commonly occurs during asbestos sampling.
Depth Filters — Depth filters are constructed usually of fibrous materials such as glass or quartz fibers. The multiple layers of randomly oriented fibers in depth filters cause their pore size to be inconsistent and undefined, therefore, a pore size rating for a depth filter is typically approximate (nominal). Particles collected with depth filters are captured within the pathways of the fibrous material. Depth filters are typically more economical and tolerate higher temperatures