The Fluval U 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. This pack contains 2 foam pads, designed for use with the Fluval U1 Underwater Filter. It maximizes bio-activity and is made from high-quality materials for long-lasting filtration.