the apparatus is an animal mattress . one embodiment is a pad made from a relatively loose pack of long particle recycled tire rubber bonded together with a polymer . the spaces between the particles provide compressibility and resiliency . the pad has corrugations on the bottom , a flat top , and is covered by a waterproof polymer fabric cover when installed . a second embodiment uses fine particles which are more tightly packed . the central section of its bottom surface is undercut to form an inverted pan - like structure . the pan sides form a support frame , and a pattern of pillars is located within the pan so that the flat top is supported but compressible .