Replacement foam filter pads for all Rena FilStar XP-Series Canister Filters. Two pack of 20 PPI (pores per inch) coarse foam filter pads, which filters large particles, such as food and plant fragments, before they enter chemical and biological chambers. Open cell design for free water flow. Place foam filter pads in the lowest part of the bottom basket in any FilStar canister filter. Rinse pads under running water every 2-4 weeks, and replace every several months.