A mold component for forming a member consisting of a nondevelopable surface, such a member being an airfoil such as a wing or the like, is provided with an interior cavity in the shape of a developable surface which approximates the nondevelopable surface. In forming the mold cavity, points of equal tangential inclination on the non-developable surface are joined by straight lines and then the areas between the straight lines are formed as flat planar surfaces, thereby to form a developable surface which is an approximation of the nondevelopable surface. A flat planar development is then formed from this developable surface and bends are made therein at the straight lines in order to form thereby the mold cavity. A substantial number of said bends extend non-parallel to each other and none of the bends intersect.