A method of reinforcing a multi-wall bag, such as one used to hold particles or powder using corrugated or fluted cardboard supports as well as the reinforced bag itself. The reinforced bags may be stacked horizontally or vertically. The supports are preferably constructed from flat cardboard, but may be constructed from plastic or any other suitable material. The supports may remain flat, or they may be scored perpendicular to the flute direction in such a way as to bend when pressure is applied along the flute direction. The scoring does not penetrate through the entire depth of the cardboard. The supports may be inserted into the bag either along the sides of the bag or along both the sides and bottom of the bag. They may also be attached to the outside of the bag along the sides and bottom in the same manner. A hybrid bag is possible wherein some of the supports appear inside the bag, and others appear outside the bag.