The Postura GelFoam Cushion provides the most advanced pressure-relieving therapeutic support and positioning available. The Postura GelFoam cushion has a layer of viscoelastic gel sandwiched between layers of dual firmness foam. The GelFoam cushion works well on wheelchairs or ordinary seats to relieve pressure buildup. This cushion comes with a fluid resistant cover and it has a non-slip bottom. The Postura GelFoam cushions come in 3 sizes: 16"x16", 18"x16", or 20"x16". The cushions are sold in 3 packs.