Mithral Armour

Armour (medium or heavy, but not hide)

Rarity: Uncommon

Mithral is a light, flexible metal. A mithral chain shirt or breastplate can be worn under normal clothes. If the armour normally imposes disadvantage on Dexterity (Stealth) checks or has a Strength requirement, the mithral version of the armour doesn’t.

Source: Player’s Handbook