The Evolution is an excellent air cushion option for those needing a high level of pressure relief. The Evolution has some unique features for an air cushion. Unlike other air cushions, the Evolution's air bladder is encased in foam. That means you will be able to sit on a stable, even foam base instead of individual cells that may move around causing you to feel unstable. The foam is sectioned in various densities to provide positioning, securement, and comfort. An adjustable valve allows you to adjust the air bladder to your personal comfort and desired level of pressure relief. The adjustable air valve also frees you from needing an air pump to inflate the cushion.