Robes of Atom's Devoted

The Robes of Atom's Devoted is a piece of clothing that can be obtained in the Fallout 4 add-on Far Harbor.

Characteristics
The Robes of Atom's Devoted is a piece of clothing that appears visually similar to other variants worn by the Children of Atom. It can not be worn with other armor pieces (excepting helmets), but it can be upgraded with Ballistic weave.

While the base effects include an extra +5 Radiation Resistance over standard Children of Atom rags, an unmarked effect is this resistance value increasing as the wearer becomes more irradiated, eventually maxing at greater than 2500 rad resist, making the wearer practically immune to environmental radiation at the expense of having an extremely low health pool. However, this effect changes once the wearer becomes even more irradiated, which can be accomplished by consuming items that irradiate the user such as Irradiated blood or Durable sludgepak. Once the player has surpassed this radiation value, almost filling the entire health bar with red, the effects shown in the Pip-Boy do not change but the player becomes completely immune to radiation and health can be restored as normal back to maximum HP. Consuming irradiated items will cause no ill effect from radiation (despite still showing rad numbers upon consumption) and geiger counter clicks and rad number display from environmental radiation will no longer occur. However, the health bar is almost entirely red and is no longer an indication of current HP, so this must be checked in the Pip-boy.

Once immune to radiation, the clothing must be worn at all times and the player's radiation level must not be lowered to maintain the effect. RadAway, Solar Powered rank 2 during the day, etc. can remove the unique clothing effect by causing the player's radiation level to drop below the threshold value. Once the effect is removed, the player's HP immediately drops according to standard radiation effects. Wearing power armor initially appears to work, but as power armor replaces all clothing bonuses the effect is removed and actual HP follows standard radiation rules despite the Pip-boy and heads-up display. Leaving power armor or re-equipping the Robes after removing them will reintroduce its special effect as long as the player's radiation level is past the trigger threshold, but any health lost will need to be healed.

Due to this robe's unique undocumented effect once upgraded with ballistic weave to protect from creature encounters it can become a viable armor for traversing the Glowing Sea, as the environmental radiation in even the most irradiated zones becomes harmless to the player and HP can be maintained at the maximum amount if the unique effect is active.

Location
A quest reward of Visions in the Fog.