BMP's Silt Sack is installed underneath Catch Basin grate to filter sediment filled rainwater running from your job-site. The rainwater and sediment fall into the catch basin and filter through the Silt Sack. They are very similar to the Orange Catch Basin Sack however they are deeper, which allows them to hold more soil and sediment. They are very easy to use and maintain for any project. The Silt Sacks come in low flow (black fabric) and high flow (yellow fabric)This product is manufactured and distributed by BMP Supplies.