Armor Plates

Armor Plates are a damage reduction buff that is granted by your shield.

Amount

Amount of armor plates are determined by the rarity of a shield.

TODO VALUES

Types

Armor Plates

Indicated by a yellow shield on the top-left of the screen near your health and over the heads of enemies. Each plate of armor reduces incoming damage by 10 percent. Plates can be destroyed with biological effects or bypassed with radiation. Damaged armor can be repaired at stations or by certain stims.

Ablative Armor

Ablative Armor is temporary Armor Plates that is added from perks, spikes, stims and other effects. Ablative armor always reaches the level of the highest effect applied rather than stacking. Ablative armor cannot be repaired.

• Armor is a new damage-mitigating buff granted passively by shield equipment and temporarily by perks, stims, or spikes. Unlike shields, armor does not regenerate when excessive damage breaks it but it can be repaired at extraction points.
• Armor repair stations have appeared all over the Bay Area. Travel to any fast travel point to find a station.

Each armor plate has an invisible "durability" value. All weapons deal durability damage in addition to their normal damage. Most weapons deal 10% of their damage to durability. Bio weapons deal 125% of their damage to durability. (Other damage types shooting an enemy who has a bio DoT on them deal 100% of their damage to durability.) 

Durability damage is not reduced by armor. It is just applied as a flat value to the durability of the "active" armor plate. So even against an enemy with 10 plates (100% damage mitigation) all weapons are dealing damage to plates, and bio weapons are tearing those plates apart.

Source