Armor Penalty
Armor (and shields) causes problems. It is heavy and cumbersome. The Armor penalty is a representation of this fact.
The following penalties apply:
The Armor Penalty applies to all Acrobatics, Athletics, Stealth, and Sleight of Hand checks. The penalty is doubled for swim checks. This is in addition to the penalties incurred as a result of the weight of the armor.
Armor which drops below 1/2 HP doubles its armor penalty, if any.
Movement costs increase by 1 AP for every 2 points of Armor Penalty. This includes actions such as standing from prone and hunkering down behind a shield.
All armor penalties stack. If one is wearing two types of armor and carrying a shield, all three penalties are incurred.
A character who wears armor and/or uses a shield with which she is not proficient takes the armor’s (and/or shield’s) armor check penalty on attack rolls and on all Strength-based and Dexterity-based ability and skill checks. Like normal, this stacks with everything.
Some armors and shields take additional penalties to certain actions, especially Move Silently. This is noted in the description.