Arcane Armor Mastery

Combat

You have mastered the ability to cast spells while w­earing armor.

Prerequisite: Arcane Armor Training, Medium Armor Proficiency, caster level 7th.

Benefit: As a swift action, reduce the arcane spell failure chance due to the armor you are wearing by 20% for any spells you cast this round. This bonus replaces, and does not stack with, the bonus granted by Arcane Armor Training.

Source: Pathfinder Core Rulebook