Some embodiments are directed to a structural element having a planar portion and at least one integral, formed edge portion. The structural element includes at least one elongated member and a formed 3-layered cardboard panel. The formed 3-layered cardboard panel includes a first and second external high density cardboard (HDC) sheet sandwiching a low density cardboard (LDC) layer between them, at least one edge-forming segment absent the second HDC sheet and the LDC layer, and planar segments flanking the edge-forming segments. An inner face of the first HDC sheet of the of the edge-forming segment is folded over and tightly associated to an external surface of the elongated member such as to envelope a top portion thereof to thereby define the formed edge portion. The planar segments is fixed to one another to define the planar portion.
