The patented Radiant Warming Inserts are designed for use with the Four Paws K-9 Keeper Sleepers.  Simply place the insert in the zippered back of crate pad.  The insert works naturally with the pet’s body heat, reflecting the heat directly back into the crate pad and keeping your pet warm and toasty.  Available in 6 sizes to fit all styles of K-9 Keeper Sleepers.