The Fluval® Foam Pad captures large particles and debris for effective mechanical filtration, the crucial first stage in the filtration process. Custom-sized, it fits 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. Includes 2 foam pads. For the Fluval® U2 Underwater Filter.