Fluval "U" Bio-Foam Pad. Fluval Foam Pad captures large particles and debris for effective mechanical filtration, the crucial first stage in the filtration process. It is custom-made to fit perfectly inside the filter chamber to prevent debris bypass. The foam pad has a pore size that allows efficient water flow, less clogging and long-lasting filtration. Suitable for freshwater, marine or reptile environments. Key Features : Captures large particles and debris for effective mechanical filtration Custom-made to fit perfectly inside the filter chamber to prevent debris bypass Has a pore size that allows efficient water flow, less clogging and long-lasting filtration Suitable for freshwater, marine or reptile environments Available Sizes: U1 Foam Pad: For Fluval U1 Underwater Filter (1 Pack) U2 Foam Pad: For Fluval U2 Underwater Filter (2 Pack) U3 Foam Pad: For Fluval U3 Underwater Filter (2 Pack) U4 Foam Pad: For Fluval U4 Underwater Filter (2 Pack)