Note: Also see my Best Arc'teryx Jackets article.
After taking it down years ago, Arc'teryx finally decided to bring the once-loved Nuclei FL back to life in February 2020.
I immediately rushed out and got one.
The overall design roughly remains the same. Outer fabric is updated to be lighter (from Arato 20 to 10), and the hood is now helmet compatible - pleasing news for climber folks.
The outer fabric is still extremely pleasant to touch, and the fit is still great (I'm 5'11", 175 lbs, athletic build - and size M fits me like a glove, see image).
Now let's take a brief look at how it compares to the Proton LT.
- Nuclei FL is much more wind resistant and a little bit warmer. Unlike Proton LT, it's also packed into its own stuff sack
- Proton LT is much more breathable and a little bit more durable
If you're looking for a summary, skip to the Conclusion & Best uses heading.
- #A sidenote here: Arcteryx.com's PDF guide to their jackets is GOOOLLDDD. Highly recommend you to check it out before you buy.
Now let's get to their bolts and nuts.
- Some of the Arc pieces you see in this post might be discontinued, and hence might be unavailable at arcteryx.com.
- If that's the case, then I'd recommend you to check out this page at REI. You might be able to find them there.
Warmth
Let's see where these two stand in terms of temperature ratings:
Here's the list of the lowest temperatures you can wear each Arc'teryx jacket without feeling uncomfortably cold.
Keep in mind that these are only approximate values assuming:
- worn over a shirt only and no shell over,
- during daily use (strolls, power walks etc at most - no high output activities),
- with light wind,
- and when it's dry out.
| Name | Est. Temp (F/C) | Insulation | Review | |||
|---|---|---|---|---|---|---|
| Arc'teryx Alpha Parka (Men's - Women's) | -17/-27 | Down | Down | No | M | |
| Feathered Friends Khumbu (Men's) | -17/-27 | Down | Down | No | M | |
| Arc'teryx Ceres SV (Men's - Women's) | -15/-26 | Down | Down | Review | Yes | M |
| Mountain Equipment K7 (Men's - Women's) | -13/-25 | Down | Down | No | M | |
| Rab Positron Pro (Men's - Women's) | -13/-25 | Down | Down | No | M W | |
| Patagonia Grade VII (Men's) | -11/-24 | Down | Down | No | M | |
| Arc'teryx Firebee AR (Men's - Women's) | -10/-23 | Down | Down | Review | Yes | M W |
| Mountain Equipment Exo (Men's) | -10/-23 | Down | Down | No | M | |
| Arc'teryx Thorsen (Men's) | -7/-22 | Down | ParkaD | Review | No | M |
| Patagonia Frozen Range (Men's - Women's) | -6/-21 | Down | ParkaD | Review | No | M W |
| Arc'teryx Centrale (Women's) | -5/-20 | Down | ParkaD | Review | No | W |
| Rab Neutrino Pro (Men's - Women's) | -2/-19 | Down | Down | No | M W | |
| Arc'teryx Therme (Men's) | -2/-19 | Down | ParkaD | Review | No | M |
| Arc'teryx Dually Belay (Men's) | 0/-18 | Synthetic | Synthetic | Review | Yes | M |
| Arc'teryx Camosun (Men's) | 0/-18 | Down | ParkaD | Review | No | M |
| Arc'teryx Piedmont (Men's) | 2/-17 | Down | ParkaD | No | M | |
| Arc'teryx Fission SV (Men's - Women's) | 3/-16 | Synthetic | Synthetic | Review | No | M |
| Outdoor Research Super Alpine (Men's - Women's) | 3/-16 | Down | Down | No | M W | |
| Patagonia Tres 3-in-1 (Men's - Women's) | 3/-16 | Down | ParkaD | Review | No | M W |
| Arc'teryx Radsten (Men's) | 3/-16 | Synthetic | ParkaS | No | M | |
| Patagonia Fitz Roy (Men's - Women's) | 3/-16 | Down | Down | No | M W | |
| Rab Electron Pro (Men's - Women's) | 5/-15 | Down | Down | No | M W | |
| Arc'teryx Macai (Men's | 5/-15 | Down | Down | Review | No | M W |
| Arc'teryx Nuclei SV Parka (Men's - Women's) | 5/-15 | Synthetic | Synthetic | No | M W | |
| Patagonia DAS Parka (Men's - Women's) | 5/-15 | Synthetic | ParkaS | No | M W | |
| Arc'teryx Patera (Women's) | 5/-15 | Down | ParkaD | Review | No | W |
| Arc'teryx Cerium SV (Men's - Women's) | 7/-14 | Down | Down | Review | Yes | M W |
| Black Diamond Access Down (Men's - Women's) | 7/-14 | Down | Down | No | M W | |
| Arc'teryx Kappa (Men's - Women's) | 7/-14 | Synthetic | Synthetic | Review | Yes | M |
| Arc'teryx Prema (Women's) | 7/-14 | Down | ParkaD | No | W | |
| Arc'teryx Radsten Insulated Men's) | 7/-14 | Synthetic | ParkaS | No | M | |
| Rab Microlight Alpine (Men's - Women's) | 7/-14 | Down | Down | No | M W | |
| Patagonia Macro Puff (Men's - Women's) | 8/-13 | Synthetic | Synthetic | Review | No | M W |
| Feathered Friends Eos (Men's - Women's) | 8/-13 | Down | Down | No | M W | |
| Arc'teryx Macai LT (Men's) | 8/-13 | Down | Down | No | M | |
| Arc'teryx Seyla (Women's) | 8/-13 | Down | ParkaD | No | W | |
| Arc'teryx Koda (Men's) | 8/-13 | Synthetic | ParkaS | No | M | |
| Arc'teryx Thorium AR (Men's - Women's) | 8/-13 | Down | Down | Review | No | M W |
| Arc'teryx Kole (Men's - Women's) | 10/-12 | Down | ParkaD | No | W | |
| Patagonia Vosque 3-in-1 (Women's) | 10/-12 | Synthetic | ParkaS | Review | No | W |
| Arc'teryx Alpha IS (Men's - Women's) | 12/-11 | Synthetic | Synthetic | Yes | M | |
| Patagonia Jackson Glacier (Men's - Women's) | 12/-11 | Down | ParkaD | Review | No | M W |
| Arc'teryx Sensa (Women's) | 14/-10 | Synthetic | ParkaS | No | W | |
| Patagonia Hi Loft Down (Men's - Women's ) | 14/-10 | Down | Down | Review | No | M |
| REI Magma 850 Hoodie 2.0 (Men's - Women's) | 14/-10 | Down | Down | No | M W | |
| Arc'teryx Atom AR (Men's - Women's) | 18/-8 | Synthetic | Synthetic | Review | No | M W |
| Patagonia Downdrift (Men's - Women's) | 18/-8 | Down | Down | No | M W | |
| Patagonia Down Sweater (Men's - Women's) | 19/-7 | Down | Down | Review | No | M W |
| Arc'teryx Magnus (Men's) | 19/-7 | Synthetic | ParkaS | No | M | |
| Arc'teryx Agrium (Men's - Women's) | 21/-6 | Down | Down | No | M W | |
| Patagonia AlpLight Down (Men's - Women's) | 21/-6 | Down | Down | No | M W | |
| Patagonia Topley (Men's) | 23/-5 | Down | Down | No | M | |
| Rab Xenon 2.0 (Men's - Women's) | 23/-5 | Synthetic | Synthetic | No | M W | |
| Patagonia Silent Down (Men's - Women's) | 26/-3 | Down | Down | Review | No | M W |
| Mountain Hardwear Ghost Whisp/2 (Men's - Women's) | 28/-2 | Down | Down | No | M W | |
| Arc'teryx Cerium LT (Men's - Women's) | 28/-2 | Down | Down | Review | No | M W |
| Arc'teryx Nuclei FL (Men's - Women's) | 32/0 | Synthetic | Synthetic | Review | No | M W |
| Patagonia City Storm Down (Men's) | 32/0 | Down | ParkaD | No | M | |
| Arc'teryx Atom LT (Men's - Women's) | 36/2 | Synthetic | Synthetic | Review | No | M W |
| Patagonia Micro Puff (Men's - Women's) | 36/2 | Synthetic | Synthetic | Review | No | M W |
| Patagonia Isthmus (Men's | 36/2 | Synthetic | ParkaS | No | M | |
| Arc'teryx Proton LT (Men's - Women's) | 37/3 | Synthetic | Synthetic | Review | No | M W |
| Patagonia Nano Puff (Men's - Women's) | 37/3 | Synthetic | Synthetic | Review | No | M W |
| Arc'teryx Norvan SL Ins. (Men's - Women's) | 39/4 | Synthetic | Synthetic | Yes | M W | |
| Patagonia Nano Air (Men's - Women's) | 41/5 | Synthetic | Synthetic | Review | No | M W |
| Arc'teryx Cerium SL (Men's - Women's) | 43/6 | Down | Down | Review | No | M W |
| Arc'teryx Proton FL (Men's - Women's) | 48/9 | Synthetic | Synthetic | Review | No | M W |
| Arc'teryx Atom SL (Men's - Women's) | 52/11 | Synthetic | Synthetic | Review | Yes | M W |
| The North Face Summit Down (Men's - Women's) | Testing | Down | Down | No | M W | |
| Mountain Equipment Lightline Echo (Men's) | Testing | Down | Down | No | M | |
| Mountain Equipment Kryos (Men's - Women's) | Testing | Down | Down | No | M W | |
| Mountain Equipment Xeros (Men's - Women's) | Testing | Down | Down | No | M | |
| Arc'teryx Andra LT IS (Women's) | Testing | Synthetic | ParkaS | No | W | |
| Arc'teryx Phoria IS (Women's) | Testing | Synthetic | ParkaS | No | W | |
| Feathered Friends Helios (Men's) | Testing | Down | Down | No | M | |
| Feathered Friends Volant (Men's) | Testing | Down | Down | No | M | |
| Rab Axion Pro (Men's - Women's) | Testing | Down | Down | No | M W | |
| Feathered Friends Rock & Ice (Men's) | Testing | Down | Down | No | M | |
| Rab Valiance (Men's - Women's) | Testing | Down | Down | No | M W | |
| Rab Expedition 8000 (Men's) | Testing | Down | Down | No | M | |
| Rab Zero G (Men's) | Testing | Down | Down | No | M | |
| Rab Generator Alpine (Men's) | Testing | Synthetic | Synthetic | No | M | |
| UBR Regulator Parka II (Men's) | Testing | Synthetic | ParkaS | No | M | |
| Helly Hansen LifaLoft (Men's - Women's) | Testing | Synthetic | Synthetic | No | M | |
| Mammut Eigerjoch (Men's - Women's) | Testing | Synthetic | Synthetic | No | M W | |
| Helly Hansen Lumines (Men's - Women's) | Unknown | Synthetic | Synthetic | No | M | |
| Haglofs V Series Mimic (Men's - Women's) | Unknown | Synthetic | Synthetic | No | M W | |
| Black Diamond First Light (Men's - Women's) | Unknown | Synthetic | Synthetic | No | M W |
Liked this table?
If you did, check out this post of mine to see more Arc'teryx tables like this one, such as fill details for all down jackets.
As you see, the Nuclei FL is warmer, but if you take wind off the table, then I'm pretty sure that the Proton LT would feel just as warm as the Nuclei FL.
Breathability
Proton LT is ahead of the Nuclei FL in this department. The reason for this is actually the sacrifice the Nuclei FL makes with its incredible wind resistance performance.
Which brings me to my next point...
Weather Resistance
Almost the entire design intention of Nuclei FL is centered around one thing: Wind resistance.
Unlike most other jackets and hoodies (including the Proton LT), it lacks the baffled seams - which, typically, let the wind right into the jacket through the vacant spots.
If you live and/or perform a high output activity out at brutally windy weather conditions, this could make an incredible advantage for you.
Proton LT in action.
In terms of water resistance, on the other hand, they're comparable. Considering the fact that the Proton LT is meant to be a mid-layer more than a shell, you might expect it to perform worse than the Nuclei FL in this department.
But that's not the case. They're about the same.
So where do they stand?
Well, neither are equipped with Goretex. They certainly won't be as waterproof as some solid Goretex Arc'teryx shells, but still fairly water resistant. Their DWR coating work fine as well.
DWR is a coating.
It's basically sprayed on to the surface of these jackets as a finish. It stands for Durable Water Repellent - which means that water will be repelled under wet conditions instead of soaking into the fabric.
DWR also decreases dry time.
It's a good thing these jackets are coated in DWR, but pay attention to the fact that DWR is a coating - meaning that it will wear off over time.
Which is why you might want to invest in a DWR spray such as this one for after treatment.
As you see, there's a strong correlation between FP x FW and temperature ratings, but not more than, say, 80%. I explained why this happens here in this post of mine.
If waterproofing is a must-have for your situation, I'd recommend you to take a look at Beta LT.
Conclusion & Best uses
- The Proton LT is designed as a breathable, insulated mid-layer for high output activities out in chilly weather. Think mountaineering, ski touring, fat biking...
Its primary points are durability and breathability. This is why I picked it as my top synthetic insulated jacket.
Additionally, it does offer some weather protection, but is best paired with a waterproof shell on top in wet weather. Otherwise it risks soaking the droplets into the fabric, especially as the DWR wears off.
- The strongest point of the Nuclei FL, on the other hand, is wind-proofing.
Under windy conditions, this also makes it a warmer alternative to Proton LT. As you see, it works as a more complete stand-alone piece compared to the Proton LT.
Additionally, unlike the Proton LT, it is packable.
But...
There's one thing you might wish having: Breathability.
I hope this post was helpful for you to learn more about the jacket(s) in your mind.
Feel free to ask me any questions or provide feedback and I'll be happy to respond in the comment section below.
Guide: Insulated & Shell Jackets
Start here:
Complete list:
Also see:
Thank you for reading!
Canberk: Coming late to this post. As always your thoughts and experiences with the gear are pretty spot on. Many thanks! Teshekher ederum!
I personally use the Proton LT Hoody for my mountain-biking/higher exertion efforts and always carry a Squamish (Arc) or Houdini (Patagonia) windshell (easily pack-able, light weight, etc.) in case the winds come up.
Of course, living in Colorado, USA the chances of heavy rain are pretty unlikely, so I literally have no Goretex outer layers. That would change quickly if I were to travel to other climes.
Keep up the great work and stay healthy, safe, and sane!! 🙂
Hi! Do you think that proton lt and nuclei fl would layer well together? Wearing more windproof nuclei over breathable proton when (for example) having a little break in cold, windy conditions sounds perfect to me, but I’m not sure if nuclei has enough room for proton lt under and would it be comfortable to wear them both at once (I know I can size up but let’s suppose they are in same size) :))
Have you changed your warmth rating form the last season? I see that now Cerium LT and Nuclei FL went up by something like 7 degrees celsius in terms of lowest comfortable limit. Why?
BTW: I really appreciate your site and find it really useful.