A tubular structural profile for a construction system, manufactured starting from the folding and cutting of a sheet of semi-rigid and foldable material, with high rigidity against bending, compression and torsion, the tubular structural profile comprising an external contour which comprises 4 substantially orthogonal sections joined at fold lines, and the tubular structural profile comprising an internal section located diagonally joining two opposing fold lines in a folded position, wherein: a) the sheet of semi-rigid material has 6 rectangular, adjacent and parallel sections, separated from each other by fold lines, wherein the two central sections (1, 2) correspond to two first external sections (1, 2) of the external contour, separated by a first fold line, followed by two sections (3, 4) corresponding to two second external sections (3, 4) of the external contour, separated from the respective first external sections (1, 2) by two second fold lines (11, 12), and followed, in a symmetrical manner, by two sections (5, 6) corresponding to two internal diagonal sections (5, 6) of the tubular structural profile, separated from the respective second external sections (3, 4) by two third fold lines (13, 14); b) the sheet of semi-rigid material is configured to be folded in a single rotation direction in each fold line, with the diagonal sections (5, 6) forming an angle greater than 90° in the third fold lines (13, 14) in the folded position, and the second fold lines (11, 12) and the first fold line forming a substantially right angle; characterized in that c) the tubular structural profile comprises at least one tongue in one of the third fold lines inserted in at least one slot located on the corresponding opposing third fold line (13, 14) in the folded position to close the tubular structural profile, preventing the profile from opening during the structural performance thereof; wherein the width of the two internal diagonal sections (5, 6) of the tubular structural profile is less than the internal diagonal distance between the opposing first and third fold lines in the folded position to create a fitted space, such that when the tubular structural profile is folded around an angle profile of the construction system having two wings positionable against the respective two first external sections (1, 2), the angle profile fits into the fitted space. a) the sheet of semi-rigid material has 6 rectangular, adjacent and parallel sections, separated from each other by fold lines, wherein the two central sections (1, 2) correspond to two first external sections (1, 2) of the external contour, separated by a first fold line, followed by two sections (3, 4) corresponding to two second external sections (3, 4) of the external contour, separated from the respective first external sections (1, 2) by two second fold lines (11, 12), and followed, in a symmetrical manner, by two sections (5, 6) corresponding to two internal diagonal sections (5, 6) of the tubular structural profile, separated from the respective second external sections (3, 4) by two third fold lines (13, 14); b) the sheet of semi-rigid material is configured to be folded in a single rotation direction in each fold line, with the diagonal sections (5, 6) forming an angle greater than 90° in the third fold lines (13, 14) in the folded position, and the second fold lines (11, 12) and the first fold line forming a substantially right angle; characterized in that c) the tubular structural profile comprises at least one tongue in one of the third fold lines inserted in at least one slot located on the corresponding opposing third fold line (13, 14) in the folded position to close the tubular structural profile, preventing the profile from opening during the structural performance thereof;