Gel Cushions are primarily designed with a separate compartment on top of a foam base. However, a gel overlay is available as a reasonable alternative to enhance any wheelchair cushion by simply placing it on top. The gel used in these cushions is water based to provide a cool surface and prevent heat to build up. Gel-foam wheelchair cushions are generally more expensive than foam, but less expensive than air cushions. The separate chambers offer greater stability and floatation that relives pressure. Most are protected with a vinyl inner cover to prevent urine from affecting the cushion and are highly durable.