Abstract: The invention comprises a corrugated container for high density bulk materials. The side walls of a box or inner tube for a box are formed from two separate corrugated pieces, connected by overlapping seams. Each overlapping piece has a free end which is scored and folded to form an integral vertical support post, in the form of a vertically disposed triangular prism, the apex of which extends towards the interior of the box. The free end of each overlapping piece is tucked within the seam overlap, to secure the triangular post. The triangular vertical support posts in the side walls of the tube increase the stiffness of the side walls to prevent them from bulging under the pressure of the bulk material contained within the box. To increase the strength of the box against stacking forces and internal pressures, the inner box or tube may be placed snugly within an outer corrugated box.