A collapsible beam element is provided, including: (a) an elongated flexible structural member having a predetermined cross section; and (b) a hollow defined by the cross section of the flexible structural member, wherein the flexible structural member is collapsible so as to enable folding of the beam element from an open configuration into a packed configuration, and wherein the flexible structural member readopts the predetermined cross section when unfolding the beam element from a packed configuration into an open configuration. The beam element is preferably made of material having predetermined shape. The beam element may be used so as to construct any collapsible three dimensional construction. Amongst other possibilities, the beam element may be used as a stretcher beam or a ladder or bridge beam.