Fluval Bio Foam PadFluval Bio Foam for the Fluval 6 Series Canister Filter fits the 306 and 406 filters and serves as mechanical and biological filtration. The porous structure increases surface area for the growth of beneficial bacteria. This bio foam filter traps particles and debris and fits within the bottom basket of Fluval canister filters. Traps particles and debris Porous structure increases surface area Compatible with 306 and 406 filters