Particles larger than three microns are collected when their momentum prevents them from following gas streamlines around fibers. They leave the streamline, strike a fiber and are collected by the fiber.

    Between 1.0 and 3.0 micron size particles tend to follow the gas streamlines as they flow relatively close to fibers. A 1.0 micron particle, for example, passing within 0.5 micron of a fiber will be collected by the fiber.

    Extremely fine particles have random side-to-side movement caused by collisions with gas molecules. A 0.1 micron particle will have about ten times the Brownian movement or random motion of a 1.0 micron particle, greatly increasing the probability of collision with a fiber.