In Norse mythology, the magical chain that binds Fenrir before Ragnarök is called Gleipnir.
Unlike an ordinary metal chain, Gleipnir is described as a soft, ribbon-like binding made by dwarfs. It was fashioned from six impossible ingredients: the sound of a cat’s footfall, a woman’s beard, the roots of mountains, bear sinews, fish breath, and bird spittle. Because these things cannot normally be obtained, Gleipnir is presented as a supernatural creation.
The gods trick Fenrir into testing the binding on the island of Lyngvi. He agrees only after the god Týr places a hand in his mouth as a pledge. When Fenrir cannot break Gleipnir, he bites off Týr’s hand.
Gleipnir holds Fenrir until Ragnarök, when the wolf breaks free. It should not be confused with Draupnir, Odin’s self-replicating ring, or Megingjörð, Thor’s strength-enhancing belt.