Your armor bonus is increased to +8, and you gain damage reduction 2/adamantine. However, your base land speed is reduced to 20 feet, and you are considered to be wearing heavy armor. You have a +1 maximum Dexterity bonus to AC, a –5 penalty on all skill checks that armor check penalties apply to, and an arcane spell failure chance of 35%.
This feat must be taken at 1st level. Warforged who takes this feat cannot cast druid spells or use any of the druid's supernatural or spell-like class features. Warforged characters with this feat do not gain the benefit of any class feature prohibited to a character wearing heavy armor.
Without this feat, a warforged character has an armor bonus of +2.