Original 50 square foot filter cartridge made by Watkins Manufacturing. This filter is used for all 2018-Current Limelight Hot Tubs, with the exception of the Limelight Prism. The Limelight tubs each require two of these filters in order to filter 100 square feet of water. This filter is made from a different polyester material than generic filters to allow more gallons per minute flow per square foot of fabric.