A double-wall container comprises outer side walls integrally formed with semi-tubular ribs extending heightwise of the container and joined at their apices to the inner side walls of the container, and an outer bottom wall also integrally formed with semi-tubular ribs which extend transversely of the container and join at their apices to the inner bottom wall. The inner side walls of the container are formed with inwardly-curved corners extending heightwise of the container, and the outer side walls are formed with outwardly-curved corners extending heightwise of the container and complementing the inwardly-curved corners of the inner side walls to define therewith tubular columns at the corners of the container.