Yes, it's the armor in the vault. You only get to wear it very late in the endgame, though. While it can't be modified, it soaks up a huge amount of damage and warns you if the shield is nearing exhaustion. Thus, if you time it right you can stand directly in the rocket volley of a Deathbringer and come out completely unharmed on the other end. It's so effective that the last fight only saw me using about 5% of my health pouch, none of the potions and resistance elixiers.