Abstract: A method for forming a hollow structure having a predetermined shape from a sheet of superplastic material. The sheet is initially formed into a preform configuration. A reusable fluid inlet tube is placed in the preform configuration to define a port in fluid communication with the interior portion of the preform configuration. The preform configuration is disposed in a containment die, which defines a cavity having the predetermined desired shape. Force is applied to the containment die to temporarily seal the edges of the preform configuration without the use of welding or diffusion bonding. Once its edges are sealed, the preform configuration becomes a gas-tight envelope capable of holding fluid that is introduced through the fluid inlet tube. Fluid (e.g.