Abstract: A heavy-duty shipping container for bulk flowable materials is constructed with an inner tubular sleeve of substantially circular cross section and an outer sleeve of polygonal cross section; the inner and outer sleeves are composed of multi-wall corrugated fibreboard, each designed to accommodate and support a portion of the stacking load of a like heavy-duty shipping container; the inner sleeve being supported by a support pad initially with its upper edge extended outwardly of the upper edge of the outer sleeve; and the support pad being deformable to allow the inner sleeve to displace into the outer sleeve so that both upper edges are in the same horizontal plane after the application of a predetermined pressure of the inner sleeve.