Exposure to radiation has hardened you against the elements. You gain +15 to armor class and +10 to all resistances. Only super mutants can pick this perk.
J.E. Sawyer's Fallout Role-Playing Game
Maybe you stood next to the reactor too much. Maybe a harsh life of slavery inured you to the little scuffs and scrapes of this God-forsaken world. Or maybe you're just a certified bad ass. You gain +2 Normal DT and +2 Ballistic DT that stack with armor.
Exposure to extreme conditions has hardened you against the elements. You gain 5 to armor class and 7% to all resistances. Only feralkins and sylvants can pick this perk.