You have learned to access the power of more than one suit or armor.
Prerequisite: Con 15; armor training II class feature; proficiency in light, medium, and heavy armor
Benefit: You may wear both a set of light magic armor and heavy magic armor simultaneously (the magic light armor is worn as part of the underlayers for the set of magic heavy armor) and gain the benefit of magic abilities from both.
Wearing both a light and heavy suit of armor has consequences. Your armor bonus is equal to the heavy armor’s armor bonus (including magical enhancement) +1. You gain no benefit from the light armor’s enhancement bonus. Your armor check penalty is equal to the worse of the two penalties –1. Your maximum Dexterity bonus to AC is equal to the worse of the two bonuses –1 (minimum 0). For movement and special abilities, you are considered to be wearing a suit of heavy armor (even if the suit of heavy armor is usually counted as medium armor for those purposes).
You get the benefits of all the magic abilities granted by the heavy armor. You may select one magic ability granted by the light armor—this may not be any version of slick or shadow and it may not be the armor’s enhancement bonus. You gain the benefit of the selected magic ability. As a standard action, you may change which of the light armor’s magic abilities you have selected.
Normal: Normally characters cannot wear two sets of armor and, if they did, would only gain the benefit of one set of magical abilities.
Adventurer’s Handbook: Genius Guide Volume 1