Rad Resistance

Rad Resistance is a Fallout, Fallout 2, Fallout 3 and Fallout Tactics Perk.

Fallout, Fallout 2 and Fallout Tactics
You are better able to avoid radiation, and the bad effects radiation causes. Each level of this Perk will improve your Radiation Resistance by 10% (Fallout) or 15% (Fallout 2, Fallout Tactics).

Fallout 3
Rad Resistance allows you to -- what else? -- resist radiation. This perk grants an additional 25% to Radiation Resistance.

This stacks with Rad-X.

The necessity of this perk is questionable as the perks gained from The Pitt (DLC) will grant 13% radiation resistance in total, the Cyborg perk will add 10% more as well as providing other useful effects and at the same time, each point in Endurance also nets a natural resistance of 2%. All power armors (not including Tribal Power Armor and Ashur's Power Armor increases radiation resistance as well (ranging from 10 to 25%). Even if the player should encounter heavy doses of radiation, Rad-X and Rad Away is of no shortage, as well an Advanced Radiation Suit can be obtained. Without this perk, it is still incredibly easy to reach the 85% max resistance.

Added Radiation Resistance from The Pitt (DLC) may dwarf out the need for this perk, though PS3 users will see use, and so may PC + Xbox360 users, though only if they do not buy the DLC.