Dirt particles become trapped in the porous foam material. At the same time, the material offers a large colonisation surface area for the purification bacteria. Even after a short maturation period the foam cartridges perform not only mechanical water purification, but also biological decomposition of harmful substances.
The cartridges by EHEIM are reusable several times over. To clean them, simply rinse them and squeeze them out, so that the bacteria cultures are not completely destroyed.