Negating explosive damage
A significant chunk of the game's greatest dangers are explosive. Starting from universal world destroyers aka. explosive cars, through rockets, grenades and ridiculous explosive turrets, up to scorched beasts ranged attacks and the explosive spam other players will share with you, things that go boom are one of the most potent challenges before you, hence, they should be dealt with.
There are two main methods of negating explosive damage. First, the Fireproof Perk Card, that reduces the damage by 45%. It's mostly mandatory, and for Power Armor builds serves as the only possible source of explosive damage negation.
Then, the Dense chest mod for non-power-armor sets. Some builds prefer to instead reduce stagger or negate the burning effect, but it's rather exotic approach and the default choice is Dense. You might need to find someone capable of modding your chest as the plans for Dense mods are quite rare and expensive.