Frodo’s protective shirt in J.R.R. Tolkien’s The Lord of the Rings is made of mithril.
Mithril is a fictional silvery metal described as exceptionally light, strong, and valuable. Bilbo receives a mithril coat from Thorin’s company after the events of The Hobbit, and he later gives it to Frodo. In Moria, the shirt protects Frodo when he is stabbed by an Orc captain, helping save his life.
The word mithril comes from Tolkien’s invented Sindarin language and is commonly interpreted as meaning “grey glitter.” The metal is associated especially with the Dwarves, who mined it in Khazad-dûm. Its rarity and properties make it one of the most prized substances in Middle-earth.
Mithril is sometimes confused with other fictional metals in Tolkien’s writings, including galvorn, a dark metal described in the later First Age material. However, Frodo’s famous mail shirt is specifically mithril.