Atom's Bulwark

Atom's Bulwark is a unique piece of armor in the Fallout 4 add-on Far Harbor. It is a legendary arm or chest piece of Marine armor.

Characteristics
It provides a Damage Resistance and Energy Resistance of 15 at 0 Rads, equal to combat armor.

Damage Resistance and Energy Resistance both increase linearly according the following: every time your current Radiation level increase past a 10% threshold of your total health, your total Damage Resistance and Energy Resistance will both increase by 5. Specifically, if 10% of your health bar is taken by radiation, you will gain 5 DR and ER. If 90% of your health bar is taken by radiation, you will gain 45 DR and ER.

Location
Rewarded by visiting High Confessor Tektus after completing Reformation or after destroying Far Harbor in Cleansing the Land.