Fluval Foam InsertFluval Foam (4 plus 4 pack) provides mechanical straining of particulate waste. It prevents particulate waste from prematurely clogging other filter media in the module stack. Durable foam filters Traps particles and debris Prevents waste from clogging other filter media Although the primary purpose of Fluval Foam is mechanical filtration, biological activity will eventually occur within its pore structure. Size: 9" X 3. 25" X . 75"