Fluval U4 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: For Fluval U4 Underwater Filter 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 Includes 2 foam pads