To prevent the early fatigued deterioration of a bag body surrounding wall by providing at least a part of the internal or external surface of a bag body with a reinforcing elastic material for restricting the bending of the surrounding wall.
A reinforcing elastic material 34 formed to have a rectangular cross section using urethane foam or soft rubber is housed and held in a tubular part positioned within the internal bag 8a of a mounting sheet 33, and integrated with the internal surface 8a of the internal bag 8a. Also, the reinforcing elastic material 34 has larger rigidity than each of sheets 31 and 32, and such softness as not causing a feeling of physical disorder on a user. When a user places his/her body on the upper surface of an exterior material and his/her load is applied to a water bag 7, this water bag 7 is deformed, due to his/her load. In this case, however, the surrounding wall of the internal bag 8a is reinforced with the reinforcing elastic material 34, and prevented from being bent at an acute angle, even when repeatedly subjected to his/her load.
WADA NORIYUKI
KAWAMURA SHOJI
