In decubitus-endangered areas, resting pressure of body and limbs, operates switches. Associated circuits control local behavior of filling in an underlay beneath the patient. Preferred features: The auxiliary circuit switching pressure, is above or below the capillary blood vessel closure pressure. An energy or flow is switched. This alters filling characteristics or flow. Electrical switching takes place, influencing filling properties. Heating is caused. The circuit switched affects filling properties directly. The circuit is switched directly. Switch contacts are mechanically actuated. Further switching variants are indicated. Switch array density is 1/mm<2> to 1/400 mm<2>. Heaters are integrated into the filling as meandering structures or miniaturized elements contacting e.g. a filling gel in various ways to alter its properties. Temperature-sensitive gels and/or liquids are used for filling, their phase transition temperatures being in the range 15 deg C-70 deg C. Gel phase transition temperatures are modified by addition of electrolyte and/or removal or materials and/or ions. The filling comprises rheological materials, especially including electro-rheological fluids.