These replacement refills are designed for use with the ProSelect® Cooling System that attaches to either the Standard or Deluxe Crate Fans. The refills are specially designed, non-toxic freezer-pack inserts that fit in the plastic housing cartridge of the Cooling System. This housing snaps onto the front of either the ProSelect Standard or ProSelect Deluxe Crate Fans to add extra cooling power that lasts for up to two hours. We recommend attaching the Cooling System to the outside of the crate only.