Choose a type of medium exotic armor, such as interlocking scale or tumbler’s breastplate. You understand how to wear that type of exotic armor properly.
Prerequisite: Armor Proficiency (medium).
Benefit: You are proficient with a specific type of medium exotic armor and take no armor nonproficiency penalties when you wear it. (See the Armor and Shields table.)
Normal: A character who is wearing armor with which she is not proficient applies its armor check penalty on attack rolls and on all Strength- and Dexterity-based ability checks and skill checks.
Special: You can gain this feat multiple times. Each time you take the feat, it applies to a new type of medium exotic armor.
A fighter may select Exotic Armor Proficiency as one of his fighter bonus feats.
Source: Races of Stone, page 139. This feat officially superseded the first version of the feat that appeared in Underdark (page 25), a Forgotten Realms® game supplement published 10/2003, making it a version 3.0 book rather than a 3.5 one. For clarity, it was then separated for Archive Three-Five into three distinct feats: Exotic Armor Proficiency (light), Exotic Armor Proficiency (medium), and Exotic Armor Proficiency (heavy).