Abstract: A method and apparatus for minimizing or eliminating warp in corrugated board by imparting different curvature on alternate successive lengths of the board being manufactured prior to its being stacked. The corrugated board, as it moves through the manufacturing apparatus, is subjected to treatment on its upper surfaces at different intervals that the lower surfaces to impart various curvatures to the sections being cut and stacked. As the cut corrugated board sections are accumulated in the stack alternate groups of board sections have opposite curvature throughout the height of the stack. The stacked sections are maintained in this disposition a time sufficient for the weight of the stack to render the formed sheets substantially flat.