Features Eheim filter cartridges consist of phenol-free foam materials. They are designed to fit into their respective internal filters and can be easily replaced by hand. Filter cartridges for mechanical and biological filtration. 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.