Mithryl

Mithryl - Mithryl is a light, flexable metal. It is extremely rare, and rumored to manifest a soft blue glow in pure darkness.
Mithryl armor
Can be any Medium or Heavy armor, but not hide. A mithryl 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 mithryl version of the armor doesn’t.
Mithryl weapons
An item made from mithryl weighs half as much as the same item made from other metals. Mithryl is too light to be used for Heavy weapons. If the weapon isn’t Heavy, it becomes Light. If it is already listed as Light it gains the Finesse property. If the weapon is Two-Handed it is now instead Versatile. Mithryl ammunition it too light to be effective.
Cost
The mithryl version of a suit of armor or a melee weapon costs 200 gp more than the normal version.