Superman's greatest weakness is Kryptonite: material from his home planet of Krypton, which dramatically weakens his super powers and has the ability to cause great harm to the people of Krypton. Taking its color from the familiar bright green of this famous mineral, this shirt is emblazoned with a classic image of the Man of Steel himself, along with text urging people to, "Say No To Kryptonite." Standard men's sizes. 100% cotton. Officially licensed by DC Comics. Imported.