Abstract: The invention covers a method of and tools for producing structures from suitable materials which are sequentially formed superplastically and then diffusion bonded using forming dies that are flexible to conform to desired contours imparted to the mating dies, which can accommodate compound curvatures, and which utilize fluid pressures internal to the tool to force the dies to conform as well as to achieve forming and bonding. The tools consist of a forming die providing contoured cavities or recesses for shaping a superplastically formable component, a flexible die having a shape of the finished structure and cooperating with the forming die, a fluid container for pressure fluid to operate the flexible die, and a retaining structure that cooperates with the forming die to contain and direct the forming pressure in the desired manner.