About one third of one's lifetime is spent sleeping and a not insignificant effort has been spent attempting to achieve comfort during this time period. Many inventors have attempted to approximate the comfort that one experiences in floating in a body of water such as the Great Salt Lake in Utah. It is believed that the California Indians spent the better part of cold winter days semi floating in pools of hot mud fed by the natural warm springs. The so called "water bed" has become popular, especially in the State of California. Water beds have taken two approaches; those that provide a "floatation" or "buoyancy" effect, and those that result in a "hammock" effect. The first efforts known to Applicant to provide a "floatation" effect is disclosed in White, U.S. Pat. No. 184,487, Nov. 21, 1876. White disclosed a plurality of water tight sacks instead of a "single rectangular oblong air and water tight sack". The White bed consisted of a rigid perimeter and the entire bed was filled with the water sacks. The rigid border probably provided a "floatation" effect. On June 15, 1971, Hall received U.S. Pat. No. 3,585,356 for a water bed consisting of a single flexible substantially inelastic bladder contained by a perimeter rigid frame. Hall, appears to be the first to fully explain the "floatation" effect which results from the use of a frame which provides lateral support to the flexible inelastic bladder. Hall filled the entire bed with water resulting in an extremely heavy piece of furniture. The entire body of the person was supported on the inelastic water bladder.
The "hammock" effect water bed is discussed in the Labianco patent U.S. Pat. No. 3,840,921. Labianco taught that if a person lies on a pillow type water bag which is not supported on its sides, the top of the water bag is placed in tension and "it will create conventional bed pressure points, and will not conform and adjust properly to the different weight proportions of the upper and lower torso of the user." In effect, the body is supported in a "hammock" type attitude.
Both the laterally supported "floatation" beds and the "hammock" type non-laterally supported beds have the problem of excessive weight. More recently a great deal of activity has centered on the problem of reducing weight by providing air or foam rubber or plastic perimeters. Examples of such reduced weight beds are taught by Tobinick in his U.S. Pat. No. 3,702,484, U.S. Pat. No. 3,789,442 and 3,815,165; and Tinnel U.S. Pat. No. 4,015,299. All of these patents lack sufficient structure to provide the necessary lateral support to the flexible water container to result in a "floatation" type support. All of these beds which are combinations of unconnected foam materials, water containers and support sheathes provide a "hammock" type of support.
Reduction of mattress weight by replacing portions of the water area with lightweight foam materials has created a comfort problem in that a person lying on beds constructed in the manner of Tobinick, U.S. Pat. No. 3,789,442 and Tinnel, U.S. Pat.No. 4,015,299 can feel the edge of the foam material where it borders the cavity holding the flexible water bladder. This problem can be overcome, but not with foam mattresses which have cavities which do not provide sufficient lateral support. Hall, supra, taught that lateral support about the perimeter of the water bladder was essential. Without lateral support, a body resting therein sinks to an undesirable depth in the water. If the legs are resting on the foam at an elevation much higher than the heavier portions of the body such as the hips or shoulders, it gives the person an uncomfortable feeling and in addition he will feel the boundry between the foam and the cavity holding the water bag. This disparity in vertical displacement is even accentuated in Tobinick, U.S. Pat. No. 3,789,442 because his cavity walls are slanted.
Finally, the prior art mattresses having foam material areas and water supported areas failed to recognize the great difference in evenness of body weight and the pressure points which occur at the hips and shoulders. Under these pressure points, foam material is more compressed than it is under the arms or legs. This unevenness in support can cause discomfort over protracted periods of time unless the sleeper shifts his weight. This unevenness of support is especially apparent in Tobinick U.S. Pat. No. 3,789,442 in which the hips and legs are supported on the water bag and the shoulders and arms are supported on foam material. While the Tobinick hospital bed had the advantage that the upper portion can be raised from the horizontal without disturbing the water cavity, the level of comfort in the hips and the shoulders is quite different.