The bunker was supported by longitudinal stiffeners and transverse bulkheads. Vertical stiffeners prevent the web plate from buckling under shear stresses. It can be provided by roof joists or beam web stiffeners. The inner and outer shells had radial stiffeners and struts between them. They are longitudinally stiffened by trapezoidal stiffeners supported by cross frames at most every . Inside of each buttress are thick transverse walls that act as "stiffeners". External longitudinal stiffeners ran along the sides. Additional reinforcement is provided through the use of fiberglass stiffeners. This is because the round duct shape does not bend between circumferential stiffeners. These give vertical stiffness, without requiring added stiffeners. Finally, the stiffeners increase the resistance of the plate to buckling. Mobile Fidelity packaged their albums in heavy cardboard sleeves, inner cardboard stiffeners, and plastic liners. The plate is supported against those loads at its edges by stiffeners and beams. Other core stiffeners, such as paper and synthetic fibers, may also be used. The Hungarian bow is a fairly long, approximately symmetrical, composite reflex bow with bone stiffeners.