The present invention is a cavity for hybrid waterbeds. The side walls of the cavity are of resilient grade foam and are broader at the top plane than at the bottom plane. The hybrid waterbed cavity of the present invention retains the positive qualities found in conventional waterbed cavities of holding and retaining a waterbed mattress, and eliminates the undesirable qualities of the reduction of sleeping surface area and the creation of excess stress on the surrounding cover which occurs when conventional cavities are subjected to body weight.

A flotation mattress is provided including a retractable valve for draining and filling said mattress. The valve includes an elongated neck portion including at least one port which may be extended from the mattress to facilitate the draining and filling operations. The valve may similarly be retracted within the mattress for storage. Upon retraction, the elongated neck portion defines a well a collapsible hose adapted to be secured to said at least one port for draining and filling the mattress may be stored. A cover is provided to protect the valve when recessed in the mattress.

A mattress system includes a first section of foam material forming the head section of a mattress, a second section of foam material forming, the central section of the mattress, and a third section of foam material forming the foot section of the mattress. The second section of foam material has a load responsive characteristic different from the load responsive characteristic of the first and third sections. The central section may be replaced by an inflatable air chamber.

A waterbed which is preferably substantially rectangular and has a substantially rigid base structure supporting a substantially rigid, but somewhat flexible, wall structure in which bladder means full of water is located so that the upper surface of the bladder is preferably about level with at least most of the upper edge of the wall structure. Liner means is placed between the bladder means and the wall structure in order to prevent leakage of fluid in the event that the bladder means is punctured. A zippered mattress cover is mounted upon the wall structure and covers the bladder means.

A mattress unit for retarding the development of decubitus ulcers includes a fabric cover having therein a foam material, and includes an inflatable bladder and a control unit disposed within openings in the foam material. The inflatable bladder contains a foam material having spaced holes in it. The control unit includes a pump which can selectively supply pressurized air to the bladder, a valve which can selectively bleed air from the bladder, and a pressure sensor which can determine the current pressure in the bladder. The pressure sensor is coupled to an input of a control circuit which controls the pump and valve. The control circuit receives power from an AC/DC converter and is remotely controlled by a hand-held pendant, the converter and pendant each being physically separate from the mattress unit and being connected to the control circuit by respective cables.