A rare metallic element that was discovered by Superman in August 1949. This metallic element was dubbed "Supermanium" by The Super-Saved Club, Supermanium is a strong metal with nigh-indestructible properties, which level of indestructibility is slightly lower than Supeman's.
Although officially discovered by The Super-Saved Club, it was Superman who discovered the veins of Supermanium ore first. The metal Supermanium is so hard that any machine which is used to grind it literally shatters. Only Superman's using his heat vision can soften the substance, and only his super-strength is mighty enough to mold it, applying more "heat and pressure" in his hands than any machine could ever produce.
Superman made the bars in Lex Luthor's cell using this metal, making him unable to escape. Superman also formed a mighty cage on the "Prison Planet" Kronis that locked up Brainiac. Lex Luthor tries to free Brainiac with a few unsuccessful attempts to cut the bars of the cage.
Superman also use this metal to create his own vehicle, the Supermobile, which he used to battle the villain Amazo when Superman was powerless under a red sun's radiation.