A fluidized bead bed includes a mattress having an outer, liquid-impermeable layer to prevent body fluids from passing into a bed tub holding fluidized beads and contaminating the beads. The bed tub includes apertures near its upper edges to exhaust pressurized air from the bed tub....http://www.google.de/patents/US4768250?utm_source=gb-gplus-sharePatent US4768250 - Fluidized bead bed
