Abstract: An airbag including an expansion part accommodating inflow of expansion gas to expand a peripheral wall, and linear joining portions arranged in a region of the expansion part and constituted by joining facing portions of the peripheral wall in a linear manner. The linear joining portions include a linear base, curved portions and swelling portions. Each of the curved portions is connected to the base and curvilinearly extends and bends toward the respective base thereof. The swelling portions are arranged at tip ends of the curved portions to smoothly connect outer peripheral edges thereof to outer peripheral edges of the curved portions. With this airbag, stress concentration is reduced around the swelling portions and the curved portions at the time of development and expansion. Thus, the linear joining portions can be arranged without causing breakage of the peripheral wall during development and expansion, and reduction in volume and expansion area held down as much as possible.

Abstract: An airbag including an expansion part accommodating inflow of expansion gas to expand a peripheral wall, and linear joining portions arranged in a region of the expansion part and constituted by joining facing portions of the peripheral wall in a linear manner. The linear joining portions include a linear base, curved portions and swelling portions. The curved portions are connected to the base to curvilinearly bend toward ends thereof. The swelling portions are arranged at tip ends of the curved portions to smoothly connect outer peripheral edges thereof to outer peripheral edges of the curved portions. With this airbag, stress concentration is reduced around the swelling portions and the curved portions at the time of development and expansion. Thus, the linear joining portions can be arranged without causing breakage of the peripheral wall during development and expansion, and reduction in volume and expansion area held down as much as possible.

Abstract: An air bag (11) for a side air bag device capable of reducing the size and weight of the device (M1) while retaining a tension line (L--L) when expanded is mounted on the peripheral edge of a door opening (W) at the inside of a compartment, and is formed into a generally rectangular bag shape for covering the door opening when expanded, while being equipped with a gas inlet (19) for introducing an expanding gas. The air bag is provided with joints (22) jointing an inner side wall (12) and an outer side wall (13) partially so as to form a tension line L--L when expanded. The individual joints (22) are juxtaposed in plurality along the tension line so as to cross the tension line, and are arranged generally at vertically middle portions so as to form one expansion chamber (18) having upper and lower spaces (18a and 18b) for the expanding gas to flow therethrough.