Improved Natural Armor

(Monster Manual v.3.5, page 304, DnD 3.5)

[General]

The creature's natural armor is thicker and harder than that of others of its kind.

Prerequisite

Natural armor, Con 13

Benefit

The creature's natural armor bonus increases by 1.

Special

A creature can gain this feat multiple times. Each time the creature takes the feat, its natural armor bonus increases by another point