You are familiar with exotic armor of dwarven manufacture and understand how to use it properly.
Prerequisites: Dwarf, Armor Proficiency (heavy).
Benefit: You are proficient with battle plate, interlocking plate, interlocking scale, and mountain plate, and you take no armor nonproficiency penalties when you wear any of these types of exotic armor. (See the Armor and Shields table for descriptions of these armor types.)
Normal: A character who wears exotic armor with which she is not proficient takes its armor check penalty on attack rolls and on all Strength- and Dexterity-based skill checks.
Special: A fighter may select Dwarven Armor Proficiency as one of his fighter bonus feats.
Source: Races of Stone, page 138.