Keystone 20 micron medium sediment cartridges feature pleated construction to provide a large amount of filtration surface area and greater dirt holding capacity. In water and water-like liquids, dirt is trapped on the outside surfaces of the filter cartridge. The large surface area of a pleated cartridge greatly increases the life of the filter and allows our filters to perform in the same manner as the hard working, long lasting air and oil filters in your car. Independent tests prove that a pleated cartridge will last 2 to 3 times longer than other types of sediment cartridges.