Air-fluidized beds have been available since the late 1960's and were originally developed for use with burn patients. These products consist of ~ 2,000 lbs. of silicon (glass) beads (75-150 m m) encased in a polyester or Gore-Tex (R) sheet. The beads take on the characteristics of a fluid when warm pressurized air is forced up through them. In some models (FluidAir (TM), KCI) the fluidization feature is variable which permits individualization based on needs and aids in the reduction of evaporative water loss. Feces and other body fluids flow freely through the sheet. In order to prevent bacteriologic contamination, the bed must be pressurized at all times and the sheet must be properly disinfected after use by each patient and at least once per week with long-term use by a single patient .