Armor Piercing

Armor Piercing (also called Armor Penetration) is an effect found on certain weapon Enchantments designed to ignore a certain percentage of the target's physical damage resistance.

Mechanics

Armor piercing reduces the target's armor resistance to your attacks by a flat percentage.

Unlike damage resistance debuffs, if the recipient of the penetrating damage has resists over the cap of 75, it will never be treated as higher than 75. This means that it is impossible to reduce the effectiveness of armor piercing (unless the victim has no armor).

Examples

You have 20% armor piercing on your bow (of Perforation enchantment), and your target has 75 (capped) resistance to piercing. Your attacks always treat the target as if they only had 55 piercing resistance instead.

The same target returns with 100 piercing resistance (effectively 75 with the cap). You will still damage them as if they had 55 piercing resistance, just like the first example.