Dragonhide

Dragonhide is a Master-level Alteration spell in The Elder Scrolls V: Skyrim. Casting the spell grants 80% physical damage reduction to the caster for 30 seconds.

Perks

 * Mage Armor - Does not affect Dragonhide as 80% damage reduction is the cap.

Spell Tome locations
Tolfdir gives the Dragonborn this spell tome at The College of Winterhold after completing the Alteration Ritual Spell quest. This quest is only availible if your Alteration skill is at least 90, the same as all other master spell ritual quests.
 * Guide to: Master Level Alteration Spells & "Alteration Ritual Spell" quest (youtube)