Abstract: A stiffened composite metal panel is made by providing a layer of metal with spaced grooves of a depth less than the thickness of the metal layer for defining separable strips of the layer and, after arranging stripes of bond-preventing material between limited portions of the respective separable strips and a second metal layer, the metal layers are passed between pressure bonding rolls with reduction in the thickness of the layer materials to metallurgically bond a portion of each separable strip to the second metal layer to form a composite metal panel while leaving a portion of each separable strip free of such bonding at the location of the bond-preventing stripe. The separable strips are then broken apart along the grooves and folded away from the second metal layer to form precisely located stiffening ribs in the composite panel.