Ultrachrome was a metal used as starship armor around the time of the Great Sith War. Silver and superconductive, it reflected blaster and slugthrower weaponry, was heavily resistant to lightsaber attacks, and was immune to metal-eating fungi.
Ultrachromes resistance to lightsaber strikes was due to its superconductive nature. When the energy field of a lightsaber interacted with ultrachrome, it would be uniformly conducted across the entire solid mass, rather than be allowed to concentrate in one area and cut through. However, this also entailed that if enough energy from the lightsaber were transferred to the ultrachrome, the entire piece would melt.