SRD:Amulet of Natural Armor

Amulet of Natural Armor: This amulet, usually crafted from bone or beast scales, toughens the wearer’s body and flesh, giving him an enhancement bonus to his natural armor bonus of from +1 to +5, depending on the kind of amulet.

Faint transmutation; CL 5th; Craft Wondrous Item, barkskin, creator’s caster level must be at least three times the amulet’s bonus; Price 2,000 gp (+1), 8,000 gp (+2), 18,000 gp (+3), 32,000 gp (+4), or 50,000 gp (+5).