No matter your choice in secondary filtration media these Mesh Filter Media Bags can handle it. The ultra fine 1/8" mesh on our Fine Mesh Filter Media Bag is ideal for small filter media like carbon or barley pellets while the 1/4" mesh on the Standard and Large Mesh Filter Bags can handle heavy duty applications of large media types such as BioBalls or Filter Media Blocks. Each Filter Media Bag is made of long lasting black nylon mesh and utilizes a zipper or black draw string to keep filter media secure.