Filter media are used in all aspects of liquid and gas treatment to remove low concentrations of particulate matter from the carrying fluid. All filter media are similar, in that particle removal is accomplished by preventing a particle of a given size from passing through a screen, or mesh, of a given opening. The filter opening size is usually defined in micrometers, µm, often referred to as microns, where a micron equals 0.001 mm which converts to an opening of 0.000 039 in. A human hair averages 0.003 inches in diameter, or 76.2 µm. Most filters are sized to remove particulates ranging in size from 40 to 150 µm and are considered as tertiary treatment devices. Rapid clogging occurs if high concentrations of particulate matter are introduced into the filter. Therefore filter media are best used for polishing the stream.