The Aquascape BioBalls Filter Media Bag is a mesh bag designed to store biological filtration media for use in ponds and water features. The bag can be filled with your choice of filter media and placed into a biological filter. Made of strong nylon material, the bag is extremely durable, providing year after year of reliable use. The large size is able to hold a significant amount of filter media while allowing sufficient space for proper filtration. An integrated drawstring helps keep filter media secure inside the bag. .