The objective of this study is to investigate the possibility on the variable thermal resistance of fiber bulk materials as a heat insulating mattress for keeping a human being warm and comfortable independent upon the change in the environmental temperature. The system for maintaining the optimum thermal condition in the bed was realized by varying the porosity of the fiber bulk materials using the deformation of the wires of shape memory alloy by the temperature change.
The relations between the porosities and the apparent thermal resistances of the typical three kinds of fiber bulk materials were measured. As a result, it was clarified that the possible variable range of the apparent thermal resistance is about the double for the bulk materials of cotton and polyester fibers. The mixing of the fine metal wires, which is a substitute for shape memory alloy, had little effect on the thermal resistance in the range of the mixing fraction.
Furthermore, the considerations on the thermal characteristics of fiber bulk materials were performed using the numerical analysis assuming the heat conduction and the radiation heat transfer. Finally, experiment of the change in the volume of fiber bulk materials and in the heat resistance was carried out actually by mixing the fine wires of shape memory alloy.