In general, magic armor protects the wearer to a greater extent than non-magical armor. Magic armor bonuses are enhancement bonuses, never rise above +5, and stack with regular armor bonuses (and with shield and magic shield enhancement bonuses). All magic armor is also masterwork armor, reducing armor check penalties by 1.
In addition to an enhancement bonus, armor may have special abilities. Special abilities usually count as additional bonuses for determining the market value of an item, but do not improve AC. A suit of armor cannot have an effective bonus (enhancement bonus plus special ability bonus equivalents, including those from character abilities and spells) higher than +10. A suit of armor with a special ability must also have at least a +1 enhancement bonus.
A suit of armor or a shield may be made of an unusual material. Roll d% to determine if it is special or standard material:
Armor is always created so that if the type of armor comes with a pair of boots, a helm, or a set of gauntlets, these pieces can be switched for other magic boots, helms, or gauntlets.
Caster Level for Armor and Shields: The caster level of a magic shield or magic armor with a special ability is given in the item Description. For an item with only an enhancement bonus, the caster level is three times the enhancement bonus. If an item has both an enhancement bonus and a special ability, the higher of the two caster level requirements must be met.
Shields: Shield enhancement bonuses stack with armor enhancement bonuses. Shield enhancement bonuses do not act as attack or damage bonuses when the shield is used in a shield bash. The bashing special ability, however, does grant a +1 bonus on attack and damage rolls (see the special ability Description).
As with armor, special abilities built into the shield add to the market value in the form of additions to the bonus of the shield, although they do not improve AC. A shield cannot have an effective bonus (enhancement plus special ability bonus equivalents) higher than +10. A shield with a special ability must also have at least a +1 enhancement bonus.
Activation: Usually a character benefits from magic armor and shields in exactly the way a character benefits from nonmagical armor and shields: by wearing them. If armor or a shield has a special ability that the user needs to activate, then the user usually needs to utter the command word (a standard action).
The cost of armor for nonhumanoid creatures, as well as for creatures who are neither Small nor Medium, varies (see Equipment). The cost of the masterwork quality and any magical enhancement remains the same.
Most magic armor and shields only have enhancement bonuses. Such items can also have one or more of the special abilities detailed below. Armor or a shield with a special ability must have at least a +1 enhancement bonus.