We are now considering capping armor penetration at 100%. Armor could no longer go negative. We're not sure if we would do this in a hotfix or in 3.1.2. We just wanted to let anyone know who is furiously trying to acquire every armor pen item in the game.

Note that there is not a not a cap on the amount of armor that can be reduced in WoW at the moment. Also note that capping armor penetration at 100% does not mean that you can always reduce every target's armor to 0%. The tooltip says "up to" for a reason.

Yes, we understand this stat can be a little confusing.