Neuranium
this was one of the heaviest, densest metals found in the galaxy. Some gravity-sensitive species claimed to be able to feel a small warping of the space-time fabric of gravity when close to a large piece of neuranium. Among its most useful properties was the fact that even a millimeter-thick piece of neuranium was impervious to sensors. Although this might have been a boon to smugglers and other criminals, the weight of enough neuranium to protect a hidden item or to line a cargo hold would have been prohibitively heavy.