Mithral

Mithral is a rare silvery, glistening metal that is lighter than iron 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.

Mithral Armor Properties
All of the following armor benefits are changes to the base item, and do not count as item properties (very important for the purpose of adding enchantments):
 * Heavy armors are treated as medium armor.
 * Medium armors are treated as light armor.
 * Light armors are still treated as light armor.
 * Armor weight is reduced by about half (varies).
 * Maximum dexterity bonus is increased by 2.
 * Armor check penalties are lessened by 3 (to a minimum of 0).
 * Spell failure chances are decreased by 10%.

Mithral Shield & Weapon Properties

 * Shields and Weapons made from mithral weigh 60% as much as normal. This weight reduction counts as an item property.
 * Spell failure chances for shields are decreased by 20% (to a minimum of 0%). This decrease counts as an item property.
 * Mithral does not affect the size category or proficiency requirements for shields and weapons.