Githyanki casters are always in their armors.

Prerequisites: Githyanki

Benefit: You may cast spells, manifest powers or use class abilities in an armor that is one category heavier than your class allows. Treat no armor as being one category beneath light. You receive armor proficiency for armors one higher than your class normally allows. If you already have heavy armor proficiency your maximum dexterity allowed increases by 2 for all armor types.