Jackets

Summary

Best uses of Atom LT and Proton LT are the same: 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.

Lastly, the difference in warmth you'll see below is almost not noticeable. 

Overview

Now let's take a look at them and understand their stance in Arc'teryx catalogue. 

• Related Data Set: Estimated temperature ratings of Arc'teryx jackets

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	Insulated	Review	Discontinued?	M-W
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. 

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.

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.

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.

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.