Collapsible portable containers having a foldable wall section with shape-retaining characteristics are disclosed. In particular, collapsible, wheeled suitcases and trolleys are provided. One or more casters of a collapsible suitcase may be retractable to permit a folding region of a wall section to overlap the depth dimension of the casters when in the collapsed position. The folding region may include foldable tiers of a flexible material, each tier having at least one stable, relatively expanded position and at least one stable, relatively collapsed position; and an intervening, non-folding tier. The non-folding tier may be of the same material as the flexible tiers but stiffer due to its geometry, or it may be composed of a different, relatively rigid material.