As you can also see in my Best Arcteryx Jackets post, Proton LT (see image) is not only my choice when compared to the Atom LT, but it's also my top pick out in the entire market.
Summary
Best uses of Atom LT and Proton LT are very similar: High output activities.
You can see this in Arc'teryx's Naming Scheme Page as well - for both "Atom" and "Proton" - as well as Arc'teryx's very own Jacket Finder tool.
They still have one glaring difference though: Breathability.
Proton LT is noticeably more breathable than the Atom LT - which is why it's pretty much always my superior pick.
Unless you come across an Atom LT for, say, more than 100 USD cheaper than the Proton LT, then I really don't see any reason to get it over the Proton LT.
- It's given a dope-dyed liner,
- Given a new construction on the cuff,
- And it's now 1" (2.5 cm) longer (I contacted customer service about this, check out the bottom of this post for more information).
These differences pretty much don't change anything in practice. If anything, it's slightly more durable now, but the difference is almost not noticeable.
So, you can apply the information you see in this post to the previous version of Atom LT.
Lastly, the difference in warmth you'll see below is almost not noticeable.
Overview
Now, before we get to the side-by-side comparison table for Proton LT vs Atom LT, let me reveal their warmth ratings first:
Find below the lowest temperatures you can wear each jacket without feeling uncomfortably cold.
These are only approximate values assuming:
- you only have a shirt under and no shell over,
- during daily use (strolls, power walks etc at most - no high output activities),
- with enough wind to cause an umbrella to twist in your hand,
- and when it's dry out.
| °F / °C | Insulation |
|
|---|---|---|---|
Arc'teryx LEAF Cold WX Parka SVX (Men's) | -40/-40 | Down |
|
Arc'teryx Ceres SV (Men's) | -15/-26 | Down | |
-10/-23 | Down | ||
Arc'teryx Dually Belay Parka (Men's) | -7/-22 | Synthetic |
|
Arc'teryx Thorsen Parka (Men's) | -7/-22 | Down | |
Arc'teryx Centrale (Women's) | -5/-20 | Down | |
-5/-20 | Down | ||
Arc'teryx Therme Parka (Men's) | -2/-19 | Down | |
Arc'teryx Camosun Parka (Men's) | 0/-18 | Down | |
3/-16 | Synthetic |
| |
Arc'teryx Patera Parka (Women's) | 5/-15 | Down | |
Arc'teryx Kappa (Men's) | 7/-14 | Synthetic |
|
8/-13 | Down | ||
10/-12 | Synthetic | ||
Arc'teryx Magnus Coat (Men's) | 14/-10 | Down |
|
17/-8 | Down | ||
19/-7 | Synthetic | ||
23/-5 | Synthetic | ||
24/-4 | Synthetic | ||
40/5 | Down | ||
43/6 | Synthetic | ||
50/10 | Synthetic |
Read more about this chart here in my Insulated Outerwear Temperature Ratings Guide.
Also see: Ultimate Arc'teryx Spreadsheet
If you think you run warmer or colder than the average person, then shift temperature ranges accordingly.
Also check out my ultimate guide to Arc'teryx Jackets.
 |  | |
MSRP | 299 USD | 259 USD |
Overall Score | ||
Arcteryx Proton LT Hoody | Arcteryx Atom LT Hoody | |
Bottom line | Best choice for those who'll be using the jacket both in the town & during high output activities | Top alternative to Proton LT |
Arcteryx Proton LT Hoody | Arcteryx Atom LT Hoody | |
Warmth Comfort Weather & Abrasion Resistance Breathability Style | ||
Arcteryx Proton LT Hoody | Arcteryx Atom LT Hoody | |
Weight | 375 g (13.2 oz) | 415 g (14.6 oz) |
Insulation Materials | 65g Coreloft Continuous | 60 g/m2 Coreloft |
Arcteryx Proton LT Hoody | Arcteryx Atom LT Hoody | |
Face Fabric | Fortius Air 20 | 20D Tyono |
To be able to understand the differences between Atom LT and Proton LT products, first we need to clear out the confusion around the entire Proton line.
Addressing to this confusion is necessary since the Proton line feels somehow "undecided" or "misplaced" to most of us. I mean, before the Proton line was introduced, Arcteryx already had a line of jackets meant specifically for high output activities: The Atom line.
So why the hell would Arcteryx go the extra mile and release a completely new line instead of improving the already existing Atom line?
Some people even look at as if Arcteryx SHOT THEMSELVES IN THE FOOT since introducing two lines of products in the very same lane is rightfully considered counter productive - not to even mention the opportunity cost and the loss of extra time & resources.
You can also see this in their Arc'teryx Naming Scheme Page here, for both Atom and Proton.
What they were really thinking? Did Arcteryx really mess up or did they instead have a greater strategy behind this?
Short answer is yes, they did have a strategy. Actually, not only they had a strategy, to me (this part is subjective), they even achieved their desired results as well.
- So what was Arcteryx's real plan with the Proton line?
After hours of research & back and forth talks with the Arcteryx Team, my take is that Proton was the Arcteryx's response to the advances in breathable active insulation and shell fabrics.
For example, Patagonia's Nano Air.
This wasn't disclosed by any of the Arcteryx's representatives to my side, but now I'm pretty sure that's the case.
Yes, Atom did have a solid reputation established around the athletic users (which is the target audience), however, Patagonia's newcomer Nano Air, for example, started to receive even better reviews.
Combine it with effective marketing, and the Air quickly started to gain some attraction around the outdoors community, as well as other US based companies.
Not to even mention the patriotic side of the events - Patagonia is a US company (a population of 330 million), and Arcteryx belongs to the neighbor Canada (a population of 37 million).
In the end, higher tech products started to receive and slowly increase their shares from this target audience pool, which caused the portion that belongs to the Arcteryx to decrease.
Atom LT wasn't the single product highly dominating this pool before Patagonia released the Air. Market was divided between pieces like Polartec Alpha, Rab Strata, Atom LT etc.
And it didn't look like stopping any time soon.
My guess here is that Arcteryx tested the waters and felt that it almost became a well accepted fact in the community that Atom LT wasn't one of the best active insulation pieces anymore. [A little off-topic: I don't disagree with that statement either as you can see here.]
And the Arcteryx's maneuver to these changing environment?
You guessed that right: Introduce a BRAND NEW line of jackets. NEW means that the quality, performance metrics and characteristics HADN'T BEEN labeled by the market/target audience yet - unlike the Atom series.
We know these series as the Proton line today.
When you think about it, it makes perfect sense as well (at least to me). Why spend your time trying to change people's minds which almost already settled?
I think we all would admit that it's very difficult to fundamentally alter well-accepted facts like these, if not impossible. Arcteryx saw an opportunity to sidetrack, and took the chance.
This is also the reason why The Atom line has seen NO revisions in the time The Proton line has seen TWO. It's also revised in 2019 as well, as you can see the revised tag here.
I hope things fell into its place in your mind now.
In summary, Proton line was Arcteryx's response to advances in breathable active insulation and shell fabrics in general.
It should now be much easier for you to wrap your head around comparing Atom LT to Proton LT.
I tried to lay out all the outcomes here in this post in a non-technical language that anyone can (hopefully) understand.
In summary; design intention of these jackets are very similar, with Proton LT being superior to the Atom LT (especially in terms of breathability). Unless you've came across an Atom LT for, say, 50-100 USD cheaper than the Proton LT, then I'm pretty sure I'd recommend the Proton LT to all of you.
That's why, for high output activity uses, I'd recommend the Proton LT. For stationary use; if you want extra warmth, get the Atom and if you want extra weather resistance, durability and better looks, get the Proton LT.
Attention here guys! Arcteryx revised the Proton LT in 2019, and the information in this post isn't applicable to the previous revisions.
I've also put this post together for the comparison between all the popular Arcteryx and Patagonia mid-layers, including the two in this post.
So if you're interested to see how well these two jackets scored in the warmth, comfort, weather & abrasion resistance, breathability and style departments; check that out as well.
Let's begin with the updates in the new Proton LT, and then we'll get to the Atom vs Proton.
Atom LT 2020 Revision: What's new?
Not much really.
With the 2020 revision, Atom LT is given a dope-dyed liner, a new construction on the cuff and is now 1" (2.5 cm) longer.
So, as a result;
- Cuff construction allows for easier on/off and layering,
- Durability is slightly increased now owing to Dope-dyed liner (Dope Permeair™ 20 - 100% nylon) - but the difference is really not noticeable at all.
Additionally, Dope Dying is much more environmentally friendly, so Arc'teryx is also reducing their mark on the planet by incorporating it into the production process.
Proton LT 2019 Revision: What's new?
The intention behind the revision Proton LT received in 2019 was to make it an even higher air-permeable insulated piece - in order for it to be able to compete against the Patagonia's Nano Air.
Fortius 40 vs 20
In order to increase breathability, designers decided to change the insulation material from Fortius 40 to Fortius 20. In English: Fabric is now slightly thinner but also more air-permeable.
This is measured with a metric called CFM (cubic feet per minute). The new Proton LT has a CFM of 40 compared to the CFM of 20 that belongs to the older version.
Coreloft Continuous vs Compact
Because the Coreloft Compact of the revised (new) version is composed of highly crimped fibers, it's more compressible and air-permeable compared to the Coreloft Continuous of the previous version.
The Coreloft Continous, on the other hand, has more fluff at the beginning (so slightly higher CLO value - which means slightly warmer) but can pack down over time meaning that the jacket will eventually lose some of its fluff and warmth a little bit.
We can say that the warmth didn't really change noticeably (if at all).
Continuous is also more durable since it's less air-permeable.
*New Proton LT on the mission.
Since the design intent of Proton LT is a highly air-permeable jacket for high output activity, design team decided to switch to Coreloft Compact for air-permeability and packability reasons.
Fit
Fit of jacket didn't get a revision with the updated model.
Results
Compared to the previous model, the most recent (2019) version of Proton LT is;
- lighter,
- more packable,
- more breathable,
- slightly less durable.
Now let's get to the differences between this 2019 version Proton LT and Atom LT.
Warmth Difference
Different insulators
The Atom LT contains 60 g/m2 Coreloft and the Proton LT contains Coreloft Compact (80g/m2 of insulation is used in the body and 60g/m2 is used in the hood).
Coreloft of Atom LT is more thermally efficient and less air-permeable. That's why it'll breathe less and hence, technically speaking, it does provide more warmth - even when you count in the effect of Proton LT's longer hemline (which increases its warmth).
For a stationary use, it seems like this could be an advantage that Atom has over Proton for some of you. However, in practice, the warmth difference isn't noticeable at all. It wouldn't even be inaccurate to say that the difference isn't little, and that it's flat out non-existent.
Face fabric differences
The face fabric of Proton LT is more abrasion & weather resistant than that of Atom's. Proton's smoother surface also feels softer and more pleasant in your hands.
Compared to Atom LT, having more resistant face fabrics, Proton LT is more suitable to be worn as a standalone piece (without any extra layers) while climbing, ski mountaineering, etc.
Also, both jackets are DWR applied.
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.
Now as you see...
The two takeaways here are:
- Proton LT is slightly more weather & abrasion resistant than Atom LT.
- It seems like Atom LT would feel slightly warmer than Proton LT due to decreased breathability - but the difference really isn't going to be noticeable at all.
*Camping with Atom LT.
But...
I know, I know...
THIS is what you want to ask here:
How much of a cold weather would either one be able to resist to?
Due to the subjectivity and somewhat vague nature of these metrics, this is very difficult to answer, if not impossible. It also depends on so many factors: Wind, layers, fit, humidity.
And did I say subjectivity?
Having said that...
To give you a rough idea about the warmth they'll provide (without any extra layers) none the less... with only a long sleeved shirt underneath:
- Atom LT would be able to just stand up against most of the "infamous" Detroit winter (around low 20 F's, that is, around -5 deg C) unless when it's fairly windy.
- Proton LT is slightly colder the same.
Check out the warmth chart I shared above for more in-depth information.
In other words, if you're cold inside the Proton LT; you'll be cold inside the Atom LT as well.
Breathability
...is the most noticeable difference between these jackets.
Especially with the updated (more air-permeable) version of Proton LT, now it's even more noticeable.
It uses actually breathable insulation and fabric, unlike Atom LT's fleece side panels.
Which brings us pretty much to the conclusion:
For high output activities...
Because of the reasons laid out, Proton LT works the best with high output activities (such as power walking, biking, climbing, trekking etc) and excels in moisture management and heat control.
The Atom LT is also an excellent jacket to wear during high physical activities, but you can think of it as a tad inferior model of the Proton LT. You're going to have to vent more often with it.
So I'd recommend getting the Proton LT.
For a stationary use...
You can get either one.
I, for example, really like the way Proton LT looks and the extra weather resistance & durability that comes with it - more than the little sacrifice made in the weight and warmth departments.
So I'd personally still get the Proton LT.
Let's mention some other details about these jackets.
Storage
Neither of these jackets stuff into its own pocket. Just so you know.
Fit and Cut
Proton LT offers a little longer hemline than the Atom LT - which is better.
In the looks department, Proton LT is more of my taste than the Atom LT.
Overall, the fit of the Proton LT is also a little trimmer but not as much to make it easier to layer.
Layering
I'd recommend layering either of these jackets with Arcteryx's own Beta AR jacket [Read Review].
Conclusion
In short, I'd recommend the Proton LT over the Atom LT for almost all cases. Think of Atom LT as a tad inferior alternative of Proton LT.
If you prefer videos, here's a good review of Atom LT:
That of Proton LT:
Overall, the fit of the Proton LT is also a little trimmer but not as much to make it easier to layer.
Transcript of Customer Service Chat for 2020 Atom LT Updates
- Hi there! My name is Camille, how can I help you today?
- Hi Camille. I was wondering about the updates that took place for the 2020 revision of Atom LT. Can you list all the changes, please?
- Hi there, thanks for chatting. I sure can.
- The redesign includes an update to the cuff construction for easier on/off and layering, an updated material package for enhanced durability, updated fit, and a dope dyed liner.
- What do you mean by updated material package?
- We updated the materials the Atom LT is made of, you can read a list of them here:
- Coreloft™ Compact (60 g/m² ) insulation. Highly crimped, multi-denier siliconized polyester yarn that has undergone a special process which reduces the thickness of the material by 50%, without reducing its insulation value by the same amount. Lightweight, breathable, thermally efficient 100% polyester fibre.
Tyono™ 20 denier shell with DWR treatment - 100% nylon
Stretch fleece - 94% polyester, 6% elastane
Dope Permeair™ 20 - 100% nylon - Last year's model did not include the Dope Permeair.
- How does it affect the use of this jacket in practice?
- It doesn't effect it, really - Dope Dying is much more environmentally friendly so we are reducing our mark on the planet by incorporating it into the production process.
- Overall the updated Atom saw more changes with the fit, durability and construction on the cuff.
- If anything it's very slightly more durable now.
- Which update made it more durable?
- The additional dope dyed liner.
- Ok, thanks. Lastly, how did the fit change?
- It is about 1" longer than the previous year's model.
- So other than this hem length difference, everything stays the same in the fit department?
- That's right.
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!
What do you think of the updated Fall 2019 Proton LT compared to the updated Fall 2019 Patagonia Nano Air? I think this would be a great comparison!
Craig,
Most important thing to note here is that these 2 jackets are MUCH more alike than they’re not. I’d say they’re 90% the same (except the Air looks quite ugly and Proton LT looks quite gorgeous to most people).
The scores in this chart might help you:
https://outdoorcrunch.com/synthetic-insulated-jackets/
As you see, Nano Air is a perfect technical piece. Proton LT, on the other hand, is also a perfect technical piece, but, compared to Air, it’s also more suitable for casual outgoings as well.
If you’ll be using the jacket both in the town when it’s cold out AND during high output activities, I’d recommend Proton LT.
If you’ll be using it during high output activities only, I’d recommend the Air.
Hope this helps.
Great comparison! Some notes though. I think that the new Proton has a new internal liner as well, no? If Permeair is new, then basically they changed every material in the jacket! Seems a pretty big overhaul for me. I always felt that the old Proton had a too thick outer fabric, and it could pack a bit better and breathes less than Nano Air. Preferred the Proton fit all the way. Atom LT did not do it for me (those annoying side panels).
Arc’teryx developed a lighter Proton FL at the same time with Octaloft insulation and the lighter Fortius 20 outer fabric (which it now shares with new Proton LT. I’d have to check out the new LT out if I didn’t have the old one. For now, I’ll be getting the FL for layering and maximizing the breathability.
In the meanwhile, I’d love to see Proton LT old vs new comparisons!
Just discovered Arcteryx a couple years ago, and I’m glad I did. Nothing else provides the technical details involved it making super light but warm outdoor gear in my opinion. Just curious as to how the Atom AR was rated as providing more warmth than the Cerium Lt? I have the Cerium Lt and sweat with it indoors at room temp. I know the Atom AR has slightly more synthetic insulation,, but figured as far as strictly warmth, down is warmer overall, no? If that’s the case I’m going to seriously look into an Atom AR for the future as I do prefer synthetic over down,,, mainly because with down you can never wear anything black or dark colored without feathers attaching to your sweaters etc. Great detailed review. Thank you.
Hi!
I live in Sweden and have both jackets.
You forgot to mention one important thing in difference.
The Atom LT can stand against in fairly windy conditions while the Proton LT has absolutely no wind barrier at all and you have to put on a shell. The wind blows right through the Proton.
Thank you for sharing your thoughts and experiences Janusz 🙂
Hi,
The Atom LT has been updated with the same Coreloft Compact as Proton LT this year, so with 20g less but same insulation materials, isn’t the Atom LT being less warmer but more air-permeabe in 2020?
Thanks
Where does the Gamma LT Jacket fit into this?
Thanks for the great review!
Hi Ross,
Gamma LT isn’t insulated. Check out my guide to Arc’teryx Shells if you’re interested in more information about the Gamma LT.
Hello,
love your reviews, I would like to know your opinion about the Proton LT and the Atom AR.
Which one do you recommend to wear for a daily base stand alone jacket (I live in London, so basically deal with the UK weather)
Thanks
Thank you for your comment Giuseppe!
Atom AR is warmth focused, and the Proton LT is breathability focused. Correct me if I’m wrong, but London must be freezing now haha. So, unless you’re planning to use this jacket for high output activities, I’d get the Atom AR. Perfect for stationary use. Plus: Synthetic insulated structure of the Atom AR doesn’t keeps warm even under damp weather (unlike down insulated jackets). An important point for London, if you ask me.
Anyone else noticed a size difference between Proton and Atom?
I have historically always been a small in everything Arc’teryx but not as of late.
Small in Nuclei, Proton and also the Kyanite (I know it’s a fleece but nonetheless) is dreadfully tight and I have had to go up to a medium. Small still fits perfect in both 2020 Atom iterations though. Go figure…
Hi –
It seems the Atom LT has been updated with Coreloft Compact 60gm. Have you tested this version as it would seem that this should improve the breath ability?
Thanks