Abstract: A plurality of bags filled with a product, which bags are to be stacked one upon the other so that the adjacent surfaces of the bags are pressed together by the weight of the upper bags pressing downwardly thereon, are coated with a coating means for controlling the friction between the coating means and the coextensive supporting surface of the adjacent bag. The coating means is adapted to become increasingly adhesive and cohesive when subjected to pressure, but with the cohesion and adhesion decreasing upon removal of the pressure so that the cohesion and adhesion between the supporting surfaces of the top two bags in the stack and the cohesion and adhesion between each pair of coextensive supporting surfaces is greater than the next pair above it by virtue of the increased weight of the product and the bag between them. As a result, the removal of the top bag in the stack produces a decrease in the cohesion and adhesion between the remaining bags in the stack.