Mithral

Mithral is a very rare silvery, glistening metal that is lighter than steel but just as hard. When worked like steel, it becomes a wonderful material from which to create armor, and is occasionally used for other items as well. Most mithral armors are one category lighter than normal for purposes of movement and other limitations. Heavy armors are treated as medium, and medium armors are treated as light, but light armors are still treated as light. This decrease does not apply to proficiency in wearing the armor. Spell failure chances for armors and shields made from mithral are decreased by 10%, maximum Dexterity bonuses are increased by 2, and armor check penalties are decreased by 3 (to a minimum of 0). An item made from mithral weighs half as much as the same item made from other metals.