Abstract: Described herein is a method of manufacturing components having "warren girder" or "X" core structures, i.e. those having internal support walls extending between their outer surfaces, from superplastically formable and diffusion bondable materials having different flow stress characteristics. By using materials of relatively high flow stress characteristics for the outer skin sheets of the component, and relatively low flow stress characteristics to form the internal support walls, the tendency for the sheets outer skin to bow outwards during superplastic formation at a faster rate in regions where they are the greatest distance from support walls is reduced. Consequently, the exterior of the outer skin sheets is less susceptible to the formation of recesses thereon at the point where the corresponding interior surface meets the inner support walls, i.e. the phenomenon of quilting is substantially eliminated.