A pack of 2 Fluval Foams to capture large particles and debris for effective mechanical filtration, the crucial first stage in the filtration process. Custom fit to prevent bypass, they have a pore size that allows efficient water flow with less clogging for long-lasting filtration. These inserts also enhance biological filtration. For freshwater and marine environments. For Fluval filter models: 404, 405, 406 & 407.