Your helm protects you from hard hits.
Prerequisites
Hard-Headed, base attack bonus +6, dwarf.
Benefit
When wearing a helmet, you add +1 to your AC against critical hit confirmation rolls. When a critical hit is confirmed against you, as an immediate action, you can apply half of the damage from the attack to your helmet rather than yourself, applying hardness as normal. If the damage destroys your helmet, any leftover damage is applied to you. After using this feat, you are staggered until the end of your next turn. You may not use this feat if your helmet has the broken condition or the attack ignores armor bonuses to AC.