Mithral

Known to the dwarves as truemetal, this shining silvery-blue metal is lighter than steel yet just as durable. Equipment made of mithral weighs only half as much as the same item made of normal metals, and has no Strength requirement. Additionally, armor made of mithral can be worn under normal clothes, and doesn’t impose disadvantage on Dexterity (Stealth) checks when it otherwise would. Small creatures do not have disadvantage on attack rolls with heavy weapons made of mithral.