The optional ProSelect Cooling System features a non-toxic freezer pack insert and a plastic housing cartridge that snaps onto the front of either the ProSelect Standard or ProSelect Deluxe Crate Fan to add extra cooling power that lasts for up to two hours. We recommend placing the attachment to the outside of the crate only. Additional replacement freezer pack Refills are also available and sold separately (see item ZW11036). Our Crate Fan Cooling System Cartridge is attractively packaged for resale. Patent pending.