Invulnerability

A type of Armor

Description from the Dor Un Avathar

This type of protection differs from Invulnerable Armor in that each point of Invulnerability covers the entire creature, just like the Protect spell. Unless detailed otherwise in the Monster entry, Invulnerability cannot normally be Healed or Mend in any way (the main exception to this are Amorphous type creatures, q.v.)