a substantially planar shipping container blank is configured for planar stacking to permit compact packaging but simplifies the ease of assembly into a triangular shipping container . the container blank is foldably divided into a rectangular longitudinal section , two end sections , and a closure tab . the interior surfaces of certain portions of the end sections are pre - mounted to the interior surface of the longitudinal section . by folding the longitudinal section of the blank along two pre - pressed longitudinal fold lines , the end sections of the blank automatically fold along pre - pressed angular fold lines to form a triangular shipping container . the container can thereafter be fastened shut by folding the closure tab along a third pre - pressed longitudinal fold line and affixing the tab to the exterior of the container .