How does Armour Penetration Work

[Zelathory]

I don't really understand the wording in the Glossary regarding Armour Penetration.
Say my Mage deals Cold damage to a Boss with an Armour Percentage of 30%, will Armour penetration make my Mage deal more damage similarly to cold pen ? I'm quite used to other games's Armour mechanics usually centered around Armour = less physical damage.

[Kejal]

Armor in this game is universal damage reduction. This is further reduced by more specialized resistances like elemental resistance (including physical here) or "application" based resistance (melee, ranged, magical). All different damage reductions stack multiplicativly, so if you have 30% DR from armor, 50% DR for melee and 65% DR for physical an attack with keywords "melee" and "physical" would be reduced by a factor of 0.7(from armor)*0.5(from melee)*0.35(from physical)=0.1225 or in other words an attack which would normally do 10k damage would only do 1225 damage.

So for your example armor penetration reduces armor (rating) in the same way as cold penetration reduces cold resistance.
It is hard to tell how much armor *rating* a boss has as it is only given as a percent (at level 150 10k armor rating is roughly 41% DR, 25k is 73,5% and 33k is 83%). Eyeballing a level 150 boss 30% armor is probably about 7000-8000 armor rating.

[Zelathory]

Originally posted by Kejal:

Armor in this game is universal damage reduction. This is further reduced by more specialized resistances like elemental resistance (including physical here) or "application" based resistance (melee, ranged, magical). All different damage reductions stack multiplicativly, so if you have 30% DR from armor, 50% DR for melee and 65% DR for physical an attack with keywords "melee" and "physical" would be reduced by a factor of 0.7(from armor)*0.5(from melee)*0.35(from physical)=0.1225 or in other words an attack which would normally do 10k damage would only do 1225 damage.

So for your example armor penetration reduces armor (rating) in the same way as cold penetration reduces cold resistance.
It is hard to tell how much armor *rating* a boss has as it is only given as a percent (at level 150 10k armor rating is roughly 41% DR, 25k is 73,5% and 33k is 83%). Eyeballing a level 150 boss 30% armor is probably about 7000-8000 armor rating.

Makes sense, thanks a lot for the explanation bro