Armor (Any Medium or Heavy, Except Hide Armor), Uncommon
Mithral is a light, flexible metal. Armor made of this substance can be worn under normal clothes. If the armor normally imposes Disadvantage on Dexterity (Stealth) checks or has a Strength requirement, the mithral version of the armor doesn’t.
Source: SRD 5.2.1 · CC-BY-4.0