Mithral Armor

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.
Dungeon Master´s Guide (SRD)
  1. DnD 5e Magic Items › Mithral Armor