Abstract: A cushioning device, which can be a mattress, mattress pad or seat for supporting a person by distributing force over a support area of the person's body, comprises a gel-filled flexible enclosure with variably-adjustable supportive force distribution to prevent pressure points and resultant decubitus ulcers (bed sores) in patients and others who must spend long periods of time in prone or seated positions. The flexible enclosure has flexible barriers which divide the enclosure into multiple gel-containing compartments each underlying a different portion of the supportive surface of the device and preventing the transfer of gel from one compartment to another. Selectively openable and closable ports each communicate between the interior of a respective compartment and the exterior of the enclosure for enabling the infusion or extraction of gel from a particular compartment so as to variably adjust the distribution of supportive force.