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 pieces Bag 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, black Material:nylon Size: . 15 x 20 cm/ 6 x 7.9 inches Package Contents: 12 x white filter bags 12 x black filter bags Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the a little different from the real thing. The measurement allowed error is +/- 1-3cm.