This mattress features high density memory foam with a 4.5 lb density, along with a firm support foam base that keeps dogs from sinking through to the floor. The top 1" memory foam and bottom 1" support foam create a supportive sleeping surface great for older dogs alike, especially bigger breeds and those with arthritic conditions. The mattress also features a Water-Resistant Nylon Liner which keeps damaging fluids away from the high quality foam. This liner can be especially helpful for owners of dogs with incontinence problems. This orthopedic crate pad mattress fits most standard wire crate sizes.