Laguna Filter Media Bags are perfectly sized to fit most pond filters. Placing the filter media in the bag provides an easy and convenient way of installing media inside the filter chamber. When the media is completely exhausted, you can easily remove and replace it with a new bag. The mesh material is very permeable and can hold most loose filter media, such as Laguna Peat Granules and Barley Straw. It comes complete with a fastening seal.