Fallout – Do item effects stack in Fallout 4

The Vault Suit is the correct choice.

My first character was still wearing the vault suit at level 20, despite trying a number of alternatives. This is mainly due to the suit's radiation resistance.

Other undergarments are somewhat useful due to bonuses to SPECIAL attributes, but as soon as you run into some radiation you get toasted, whereas that same radiation would have barely registered with the vault suit on. Still, these other undergarments have situational uses. Undergarments that add to CHA can be a huge help when bartering or persuading. Undergarments that add to INT are good to put on before turning in quests.

The BOS Uniform grants 5 rad resist, so that might be a possibility as well. However, you can't upgrade the BOS Uniform. This means that it is quickly outclassed by the vault suit, which can be upgraded multiple times. You could also consider wearing headgear that has rad resists, like an Assault Gas Mask, but then you miss out on the attribute bonuses from a hat and glasses and look like a goon.

Later in the game you can get radiation resistance from your armor. By level 13, you can get Armorer 2 and Science! 1, allowing you to add the Leaded Misc mod to your armor. You can easily get 50 or more rad resist without a Vault Suit at this point. That's enough for almost any situation, so you can switch to different undergarments if you like. One easily obtained alternative is the Minuteman Outfit, which adds to AGI and PER. Preston is wearing one of these, and the clothing stand I built in Sanctuary Hills has two in stock every day.

More details on available clothing here, but that list doesn't look comprehensive at this time.

I got sick of waiting for an answer to my broader question regarding how the damage multiplys in general, so I did a bunch of testing myself.

Method:

All tests were done by shooting a friendly setler in the back of the torso at close range.

The NPC was wearing nothing but a Minuteman outfit and had their HP set to 5000 with the console. I did not check what their Damage resistance was nor did I modify it, though I probably should have.

A single shot was taken, NPCs HP remaining checked with the console, then the game was reloaded. This was done 5 times.

Due to perks etc, my Sneak attack bonus was at 4.2 Not sure what my exact critical bonus is, I had 4 ranks of Tesla Science (+20% crit damage) and no other perks or mods which would increase it.

Tests performed with a Laser Rifle, instigating tests performed with Old Faithful with the same mods. Both showed a base damage of 144 in the Pip-Boy interface.

---

Results:

Normal Shot

111.81, 214.99, 213.32, 214.57, 212.48

Average: 204.72 damage (Average may be low? First shot did much less damage)

Critical Hit:

350.93, 349.86, 350.63, 350.34, 351.00

Average: 350.552

Sneak Attack:

905.80, 905.97, 906.70, 906.38, 905.46

Average: 906.062

Sneak Attack + Critical Hit:

1040.25, 1042.20, 1040.83, 1038.45, 1040.27

Average: 1040.40

Normal Shot + Instigating Weapon

425.43, 430.58, 431.57, 430.70, 352.29

Average: 414.114 damage (Average may be low? Last shot did much less damage)

Critical Hit + Instigating Weapon:

565.44, 559.52, 566.39, 565.26, 566.12

Average: 564.546

Sneak Attack + Instigating Weapon:

1810.25, 1812.87, 1813.63, 1813.38, 1812.00

Average: 1812.426

Sneak Attack + Critical Hit + Instigating Weapon:

1944.69, 1946.42, 1947.35, 1947.74, 1947.11

Average: 1946.662

---

Discussion:

The above results show some variance, with some shots noted as being much lower than others. It is not clear if this was due to poor accuracy causing some bullets to hit the wrong location (though injuries on target suggested all shots hit the back), natural RNG spread of damage, or damage resistance of the target.

When roughly comparing Sneak attacks performed with both Instigating and normal weapons, the stated Sneak Attack bonus does appear to be multiplicative with Instigating ( [Weapon Damage x2] x4.2) or at least close enough to satisfy me that this is the case.

Interestingly, Critical Hits do not appear to be multiplicative with Sneak and Instigating. In all situations the additional damage inflicted was close to the weapons stated base damage (144, give and take some variance). This suggests to me that critical strikes are seperate damage which is calculated and then added after sneak attacks and instigating are multiplied ( {[Weapon Damage x2] x4.2} + [Weapon Damage xCrit Modifier])

The Wiki suggests that Critical Hits use the following formula:

Ranged: Critical Hit Damage = DamagePaper + DamageBase x CriticalMultiplier

Melee/Unarmed: Critical Hit Damage = DamagePaper x 1.5 + DamageBase x CriticalMultiplier

DamageBase = Weapon damage, including workshop mods, but excluding perks and other bonuses. DamagePaper = Damage displayed in PipBoy (PipBoy cuts off decimal places)

Conclusion:

Sneak Attack and Instigating are multiplicative with each other.

Critical Hits are not multiplicative with Sneak or Instigating

This suggests: ([Weapon Damage x Instigating] x Sneak Modifier) + (Weapon Damage x Crit Modifier)