Filtration occur when the dirty water flow through the thin wall of the cartridge. The cartridge comes in the form of a smooth or pleated cylinder, and is inserted in the filter made of plastic material resistant to aggressiveness of water pool and pressure.

The cartridges come in two types:

• vegetable fiber: consists of a sheet of cellulose of a thickness that is placed on a support of plastic material;

• synthetic material: this is a "fabric" of polyester or similar, placed on a support of plastic material.