Conductive, NonStatic Cowl Prevents adherence of Particles to Cassette Walls for More Accurate Analysis 0.8 μm GN4 Metricel® membrane has a low fiber background count. It is widely accepted for air monitoring of fibers, asbestos fibers, and metals. Leak proof and tamper proof. Banded cassettes ensure airtight seal for critical applications. Available unassembled for cost effective monitoring with a variety of Pall membranes. The 25 mm air monitoring cassettes are conductive and nonstatic cassettes used to monitor respirable constituents, such as fibers, silica, metal, and dust.