Demonflesh

Fiendish Codex I: Hordes of the Abyss (FCI)Supplementals (3.5)
School
Transmutation
Casting Time
1 standard action
Components
V, S
Range
Personal
Target
The caster
Duration
1 minute/level
Saving Throw
None (harmless)
Spell Resistance
No (harmless)

Related

Your flesh becomes thick and leathery like a demon’s.
This spell grants you a +1 enhancement bonus to your natural armor for every five caster levels you possess (minimum +1, maximum +4).
A creature without natural armor has an effective natural armor bonus of +0.