Each cartridge is built around a double-thick polyester fiber pad wrapped over a bed of activated carbon, set inside a ribbed plastic frame that spreads water evenly across the carbon for consistent contact. The fiber pad traps debris and waste particles as tank water passes through, while the carbon works to reduce odors, discoloration, and dissolved impurities. The cartridge is fully pre-assembled and slides directly into the filter box, so no cutting, bagging, or extra assembly is needed. Rite-Size color-coded packaging is used to help match each cartridge to the correct Penguin filter model. Cartridges are intended for periodic replacement as part of routine aquarium filter maintenance. Packs contain multiple individually sized cartridges for use in compatible Penguin power filter units.