Armor Penetration and Armor resistance.

[hoplite14gr]

If we trust this source:
From Plutarch´s "Life of Demetrios"(The Besieger)
"Whilst Demetrius was at this same siege, there were brought to him two iron cuirasses from Cyprus, weighing each of them on more than forty pounds, and Zoilus, who had forged them, to show the excellence of their temper, desired that one of them might be tried with a catapult
missile, shot out of one of the engines at no greater distance than six-and-twenty paces; and, upon the experiment, it was found that though the dart exactly hit the cuirass, yet it made no greater impression than such a slight scratch as might be made with the point of a style
or graver. Demetrius took this for his own wearing, and gave the other to Alcimus the Epirot, the best soldier and strongest man of all his captains, the only one who used to wear armour to the weight of two talents, one talent being the weight which others thought sufficient.
He fell during this siege in a battle near the theatre."

Kind regards