Originally posted by Suzaku:

Just checked it now to be sure: You must wear all 3 pieces to get the fire resistance buff. The headpiece alone has no special bonuses on it except for the 3% speed buff.

Foxglovez is mistaken in their understanding of the wording on the tooltip.

Thanks for the quick response! I have not found any cultists yet, so didn't even have the recipe unlocked to look at it.