durable,breathable and corrosion resistant,great for use in canister filter system.zipper:unlike the Metal zipper, filter bag zipper is plastic,not contain metal which may rust and pollute your water,and convenient to fill and empty bags.Wide usage:this mesh filter bag fit for most kinds of filter media, like Pelletized Carbon, Balls, Ceramic Rings, Ammonia Remover,suitable for aquarium, swimming pool, pond and any other occasions.( note, it for finer particles) you for a long time usage.: 24 piecesBag zipper design: Each filter bag with a plastic zipper,so it 't rust and harm fish health,and ventilate for fish to stay inside for mesh grids,also convenient to fill and empty bags.Wide range of usage:fit for most kinds of filter media, like Purigen, Pelletized Carbon, Balls, Ceramic Rings, Ammonia Remover, suitable for freshwater and saltwater tanks,power filters.colour:White, blackMaterial:nylonSize: . 15 x 20 cm/ 6 x 7.9 inchesPackage Contents:12 x white filter bags12 x black filter bags