2 Hours / Level Barkskin makes a creature's skin as tough as bark. The effect grants a +3 natural armor bonus to AC. This bonus increases to +4 at 6th level and to +5 at 12th level and up. Since the AC bonus is a natural armor bonus, it does not stack with any natural armor the subject may already have.
Metamagic allowed
Extend, Quicken, Silent, Still
How it works
It lasts one round per caster level, and Extend doubles that.
Everyone it covers gains +4 to Armour Class and +4 to saving throws against good creatures, and spell resistance of 25, or of your caster level if that is higher.
A good creature striking one of them in melee takes 1d8 negative damage plus half your caster level.
See also
Magic - save DCs, saving throws and when you cannot cast