Shield Toughness

Note - beyond shield saves, your shield's toughness value is unlikely to be used.

Shields do not use hp. Rather, each has a toughness based on it's material and make (see below). Damage in excess of it's toughness 'damages' the shield, reducing it's AC bonus by one. If a shield takes damage greater than double it's toughness, or it's AC bonus is reduced to 0, it is ruined.
 * If a shield has a split ranged/melee AC bonus, 'damage' reduces both values by one, to a minimum of zero. The shield is ruined when both values are reduced to zero.

Properties
Metal: toughness 15 Wood: toughness 10 Masterwork: toughness +5
 * Resistances: piercing, slashing, all energy except force & thunder
 * Immunities: psychic, poison, dex-based piercing
 * Cannot shield save against lightning damage
 * Resistances: piercing, all energy except force, thunder, acid & fire
 * Immunities: psychic, poison, dex-based piercing

Super-hard metal: toughness +10

Magical: immunity to damage, except by magical weapons with an enhancement bonus higher than the shield's