Impervious

An impervious weapon is warded from damage and decay. A metallic weapon cannot rust and a wooden weapon cannot rot or warp, even by magical or supernatural means. An impervious weapon gains double the normal bonus to its hardness and hit points for each point of its enhancement bonus. The break DC for an impervious weapon and the wielder's combat maneuver defense against sunder maneuvers against the impervious weapon each gain a bonus equal to twice the weapon's enhancement bonus.