Chardalyn

This dusky gray material is a rockhard, crystalline substance as strong as metal, though considerably easier to work with than steel. Chardalyn is cold to the touch and readily accepts magical enchantment, making it an ideal substance for wands, staffs, and other magic items.
A suit of armor is made of thin, overlapping sheets of chardalyn. While you’re wearing it, you have advantage on saving throws against spells and other magical effects, and spell attacks have disadvantage against you.