Abstract: A high gas pressure material capable of producing 50-300 psi gas pressure at forming temperature is placed in an enclosed area surrounding and sealing the blanks to be superplastically formed, without the use of argon gas. The blanks are formed under tensile stress by the internal pressure produced by the high gas pressure material. The method can be performed concurrently with diffusion bonding to obtain a metallic structure from a plurality of workpieces, and also can be used to manufacture perfectly spherical hollow bodies by a dieless method.