Foam is an excellent mechanical filter media. The porous channel structure within the foam obliges the incoming water to deviate from a straight path, maximizing contact time and giving the foam a huge holding capacity for debris. This is easily observed when rinsing foam, as large quantities of waste are released. Maximum mechanical effect is achieved after approximately 10 to 14 days.

Foam also supports essential bacteria and can be a mechanical and biological filter media, as evidenced by internal filter systems, as long as a regular water change schedule is respected.