It has been suggested by Krag and Kountz (1950), Horvath et al. (1955) and Spurr et al. (1955) that the mechanism for prevention of heat loss is less efficient in the aged than in the young. In addition, they observed that peripheral vasoconstriction occurred more rapidly and more intensively in the aged people in response to the cold stimulus. Although it is not clear on the basis of these reports whether the Physical insulation of the aged people in cold would be different from the younger, it is evident that the vascular reactivity in response to cold seems to be altered in the aged people. Hence this investigation was undertaken to investigate the physical insulation of the aged people in a systemic manner by water immersion method which has been successfully applied to the Eskimos and Korean diving women by Rennie et al.