The most fundamental strategy for reducing pressure near a bony prominence is to allow the prominence to be immersed into the support surface. Immersion allows the pressure concentrated beneath the bony prominence to be spread out over the surrounding area. Immersion also increases the potential for body weight to be shifted to areas around other bony prominences. For example, when a person is sitting on a relatively hard cushion, a disproportionately large portion of the body weight is born by the tissue beneath the ischial tuberocities. On a softer surface, the protrusions of the ischial tuberocities become immersed in the cushion and weight is distributed to the area beneath the greater trochanters. With this greater immersion, the body weight is divided between these additional bony prominences and pressure is decreased. This definition of immersion does not distinguish between immersion resulting from compression of the support surface and immersion resulting from the displacement of a support surface's fluid components.

The potential for immersion depends on both the force-deformation characteristics of the cushion and its physical dimensions. For fluid-filled support surfaces, immersion would depend on the thickness of the surface and the flexibility of the cover. For elastic and viscoelastic support surfaces, the potential for immersion depends on their stiffness and thickness. Consider how the thickness of a seat cushion might limit the potential for immersion. If the thickness of a seat cushion is 1 1/2 in. and the vertical distance between the ischial tuberocities (ITs) and greater trochanters is 2 inches, the potential for immersion is not large enough to unload the ITs.