Abstract: There is disclosed a hollow reinforcing element for casting into composites, which in use defines passageways that may communicate to the exterior of the composite and that can serve as conduit arrays in structures formed from the composite. Benefits include superior strength to weight ratios, reduced thermal stresses, suppression of crack propagation, and improved corrosion protection. The hollow reinforcing elements may also be used to provide antennae, drain systems, leveling devices, containment structures and pneumatic levitation of vehicles.