Reusable foam filter box compatible with Bubble and Jetted Pure-spas, replacement for S1 cartridge. Replacing paper filter elements is part of regular pool maintenance. These washable and reusable foam filters help reduce ongoing maintenance costs. Higher initial cost compared to standard cartridges, but offers longer service life. More durable than paper filters and can be cleaned and reused multiple times. Size: 10.8 x 7.3 cm. Center hole diameter: Approx 4 cm. Material: Sponge. Color: Blue. Package contents: 18 x Filter sponges. The package includes only the items listed above; other accessories are not included. Note: Lighting and monitor settings may cause slight color variations between the product and the image. Measurement tolerance: +/- 1-3 cm.