The Aquascape Medium Density Rigid Filter Mat provides efficient mechanical and biological filtration for your pond. The filter mat measures 24" by 39" and can be easily cut to your desired size and shape using a serrated knife. This allows for installation in a wide variety of skimmer boxes and filters. Aquascape Medium Density Rigid Filter Mats are 1.5" thick and extremely easy to maintain, only needing to be cleaned periodically. For best results, we recommend combining different densities to maximize mechanical and biological filtration.