Arc’teryx Nuclei vs Proton: Temp ratings & more

Nuclei vs Proton: Overview

I have all 5 items: 

• Nuclei line: Niche products. Very warm at an instant, incredibly wind resistant and comfortable. But also not breathable at all and come with fragile outer fabrics. 
  • Nuclei (aka FL): Lesser warm Nuclei. 
  • Nuclei SV: Warmest Nuclei. 
• Proton line: Versatile all round items. Very breathable and durable. But not that warm or wind resistant. 
  • Proton Lightweight (aka FL): Least warm Proton. 
  • Proton (aka LT): Mid warm Proton. 
  • Proton Heavyweight: Warmest Proton. 

I love them all. As long as you know what you're getting, none of them will disappoint. 

Find comparisons at arcteryx.com below. 

• Nuclei (aka FL) vs Proton Lw (aka FL) vs Proton (aka LT): 
  • https://arcteryx.com/us/en/compare/X000006870/X000006908/X000007520 
• Nuclei SV vs Proton Hw: 
  • https://arcteryx.com/us/en/compare/X000007238/X000007494

First thing to note is that Nuclei are more niche products.

They're belay jackets, meaning that they're meant to be put on when you stop moving (whatever high output activity you're performing).

They're meant to get them out of the bag and put them on quick to maintain your core temp. 

That's their main purpose. That's why they come with stuff sacks, offer terrible breathability, come with fragile face fabrics that cannot resist abrasion and are cut looser. 

They are however also spectacularly warm, incredibly wind resistant and extremely comfortable with a bunch of pockets. Its outstanding warmth to weight ratio is mind blowing. 

You feel the warmth inside a Nuclei at such an instant that it's insane. Unlike Proton, you don't even need to wait for the warmth to pick up. 

This is why I look at Nuclei as down jackets that can get wet. I use them casually as well, as long as my output is none to low. 

Luckily, the SV (the warmer) does come with a two way zipper. I primarily use this for comfort reasons when sitting down or driving (keeping only the upper half zipped).

Other use of two way zipper is for dumping excessive heat. Although it's not as effective as the Atom's side fleece panels it still helps a lot. 

Proton, on the other hand, are far more versatile. They're perfect for any high output activity, including climbing and heavy backpack use where lots of abrasion is expected.

Their cutting edge face fabrics are much more developed than Nuclei. They're breathable, come with a trimmer cut and shorter hem length. 

They're durable and can better resist against abrasion. You can wear them during high output activities or casually. 

But even the warmest Proton, Proton Hw, isn't nearly as warm as the warmest Nuclei, Nuclei SV. On top of that, you've got to wait for it to heat you. 

Although Proton and Nuclei are both water resistant, when it comes to wind resistance, the Nuclei has the edge by far. 

If you rarely get jackets, you might want to get one of the Protons. If warmth and weather resistance are your only concerns, and you don't care about breathability at all, get a Nuclei. 

If you're looking for maximizing the breathability, then you should stop reading here and visit Arc'teryx Proton vs Atom guide instead. I've got all the most recent Atoms, too (Hw (aka AR), base (aka LT) and SL (soon to be Lw)) and they're the most breathable line. 

Find comparisons at arcteryx.com below. 

• Nuclei (aka FL) vs Proton Lw (aka FL) vs Proton (aka LT): 
  • https://arcteryx.com/us/en/compare/X000006870/X000006908/X000007520 
• Nuclei SV vs Proton Hw: 
  • https://arcteryx.com/us/en/compare/X000007238/X000007494

Naming changes

After changing the names of some women's jackets last season (Fall/Winter 2023), this season Arc'teryx moved on to make the same changes for men's counterparts as well.

• Nuclei FL → Nuclei
  
• Proton FL → Proton Lightweight (in short, Lw)
• Proton LT → Proton
• There's also a new arrival, Proton Heavyweight. 

Changes are exclusive to the naming and fit. Structural designs remain the same. The fit is being updated universally, for all Arc'teryx jackets. 

• Fit

I'm 5'11", 165 lbs, athletic build. Size M fits me perfectly. 

My size is always the same. Arc'teryx, Patagonia, TNF, Salomon, Columbia, Nike, Adidas, Under Armour, Zara... Doesn't matter. 

• Arc'teryx's 2024 men's fit revision

Straight from arcteryx.com on what's changed: 

Source: https://arcteryx.com/us/en/help/sizing/mens/tops/new

Not all jackets come with revised fit. Only the ones with following statement. 

• Poll

Which Arc'teryx fit do you prefer?

Legacy fit

Revised fit

• Poll

Which cuff type do you like more?

Stretch gusset cuffs

Stretch knit cuffs

Nuclei vs Proton: Warmth

Check out the table below. 

You'll see not one but two different insulation thicknesses for Nuclei SV. 

• Two layers of Coreloft (180 gsm) takes place at the front, back, and upper arms. 
• Single layer of Coreloft (90 gsm) takes place at underarms, lower arm, sides, and hood.