Adamantium. Arguably the toughest metal in the Marvel universe. It has shrugged off Hulk punches and bludgeons from Thor's hammer. The question I pose however is, would Superman be able to break/dent it? He can after all, do [url=http://media.comicvine.com/uploads/6/67064/2081435-supermansuper_strength_super.jpg]this.[/url] (Not even his greatest strength feat) I'd imagine it would be like one of those unstoppable forces meets and immovable object kind of thing. EDIT: No sundips and no punches that involve flight or speed. Just a regular ass standing on the ground punch. EDIT 2: Changed from Vibranium to Adamantium because Adamantium evidently seems more durable.