Your specialized training in armor allows you to avoid spell failure.
Prerequisite: Armor Focus
While wearing armor in the weight class selected for Armor Focus, you avoid the chance for spell failure.
Normal: Armor interferes with a spell-caster’s gestures, which can cause spells to fail if those spells have a somatic component.
Special: You may take this feat multiple times. Its effects do not stack. Each time you take this feat, you apply it to a different weight class of armor.