|This material from the 5th edition SRD is published under the OGL|
Magic Armor, (medium or heavy, but not hide), uncommon
Mithral is a light, flexible metal. A mithral chain shirt or breastplate 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.