Intangible is a decaying Buff that reduces all damage and HP loss you take to 1. It lasts 1 round for each stack of Intangible you have.
Intangible applies to all damage and HP loss. Damage from Exploders, Thorns, Poison, powers like Juggernaut, cards such as Offering, damage multipliers like Vulnerable and Slow, etc. will all come out to 1 damage per hit.