[Suicide Junkie]

To calculate how much damage will be absorbed by the armor:
(penetration factor) ^ (number of layers)


For example: 5 layers of armor that each leak 70% of the damage through (70% penetration = 0.7)

0.7 ^ 5 = 0.168

Therefore, only 17% of the damage will make it all the way through those 5 layers.