Arc’teryx Proton LT vs Atom LT

In FW23, women's Proton and Atom lines have undergone a naming scheme change. 

The suffix "LT" is removed and the suffix "AR" is changed to "Heavyweight". The change, however, is limited to the names only, with the products remaining identical. 

Naming scheme of men's counterparts also remain the same. 

The consensus when it comes to Proton vs Atom is that Proton LT is a little bit warmer than the Atom LT, owing to its loftier insulation (80 vs 60 gsm Coreloft). It's also a bit more durable and weather resistant. Atom LT, on the other hand, brings side fleece panels to the table, which makes it a little bit more breathable than the Proton LT in return. 

Keep in mind that these products are much more similar than they're different. Don't be surprised if you don't recognize any of these differences in practice. 

Links:

• https://arcteryx.com/us/en/shop/mens/proton-lt-hoody
• https://arcteryx.com/us/en/shop/mens/atom-lt-hoody
• https://arcteryx.com/us/en/shop/womens/proton-hoody
• https://arcteryx.com/us/en/shop/womens/atom-hoody
• See the side by side comparison of Proton LT vs Atom LT:   https://arcteryx.com/us/en/compare/X000004842-distortion/X000005160-oracle

Much lighter configurations of these jackets such as the Proton FL (Men's - Women's), Atom SL (Men's - Women's) and Proton Hybrid Hoody (Men's - Women's) and the heavier configuration Atom AR (Men's - Women's) have not been included in this article since they have different design intentions and best uses. 

Raw Name	Arc'teryx Proton LT	Arc'teryx Atom LT
Name	Arc'teryx Proton LT (Men's - Women's)	Arc'teryx Atom LT (Men's - Women's)
Image
Temp (°F / °C)	37/3	43/6
Breathability	7/10	8/10
Weather Resistance	7/10	6/10
Durability	9/10	7/10
Packability	5/10	5/10
Best pick for	High output activities.
Review	Review	Review
Pit venting?	No	Yes, mesh
Stuffs into itself?	No	No
Two way zipper?	No	No
Size Chart	[Men's / Women's]	[Men's / Women's]
Type	Synthetic	Synthetic
Fill Power	N/A	N/A
Fill Weight (grams)	N/A	N/A
FP x FW	N/A	N/A
Synthetic Insulator (SI)	Coreloft Compact	Coreloft Continuous
SI Amount	80 g/m2 + 60 g/m2	60 g/m²
Face Fabric	Fortius Air 20	20D Tyono
Activity	Climbing	All Round
Fit	Trim	Trim
Weight	375 g / 13.2 oz	375 g / 13.2 oz
Length (CB)	75 cm / 29.4 in	74 cm / 29.1 in
arc-mens-url	https://www.arcteryx.com/us/en/shop/mens/proton-lt-hoody	https://www.arcteryx.com/us/en/shop/mens/atom-lt-hoody
arc-womens-url	https://www.arcteryx.com/us/en/shop/womens/proton-hoody	https://www.arcteryx.com/us/en/shop/womens/atom-hoody
pat-mens-url
pat-womens-url
rei-mens-url	https://www.rei.com/product/154873	https://www.rei.com/product/175332
rei-womens-url	https://www.rei.com/product/152547	https://www.rei.com/product/174720
backcountry-mens-url
backcountry-womens-url
amazon-mens-url	https://www.amazon.com/Arcteryx-Proton-Jacket-Glade-Large/dp/B08BJFXW1J	https://www.amazon.com/Arcteryx-24109-Atom-LT-Jacket/dp/B08BJHB631
amazon-womens-url	https://www.amazon.com/Arcteryx-Lightweight-Breathable-synthetically-Insulated/dp/B0973FDVWV	https://www.amazon.com/Arcteryx-24112-Atom-LT-Jacket/dp/B08BJFFFB4
image-url	https://images.arcteryx.com/F22/1350x1710/Proton-LT-Hoody-Distortion.jpg	https://images.arcteryx.com/F22/1350x1710/Atom-LT-Hoody-Forage.jpg

If you're interested in reading more about them, too; click through: 

• https://outdoorcrunch.com/arcteryx-proton-hybrid-hoody-review/
• https://outdoorcrunch.com/atom-ar-vs-atom-lt/
• https://outdoorcrunch.com/arcteryx-atom-lt-vs-sl/
• https://outdoorcrunch.com/atom-sl-vs-proton-fl/

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. 

I'd recommend you to base your decision when it comes to Proton LT vs Atom LT primarily on what you're planning to do with the jacket, your view when it comes to side fleece panels, and lastly, your taste when it comes to the looks. 

Because of superior warmth and abrasion resistance capability of Proton LT, I think that it's mostly the better pick for climbing and skiing in not-so-cold-but-still-chilly days.

Atom LT, on the other hand, is mostly the better choice if you run warm and would love side fleece panels for increased breathability. 

Now let's get to the differences between this 2019 version Proton LT and Atom LT.

Warmth

Both Atom LT and Proton LT use Coreloft Compact. But Proton LT is equipped with 80 gsm of it in the body and 60 gsm in the hood, whereas the Atom LT is equipped with 60 gsm everywhere. 

On top of that, side fleece panels of Atom LT make a great job in terms of increasing breathability, but in return, this also causes the heat to escape. 

Proton LT also comes with slightly longer length, which makes a noticeable difference in warmth. 

Weather resistance

The face fabric of Proton LT (Fortius Air 20) is more abrasion & weather resistant than that of Atom's (Tyono 20). The suffix number in the end represents the denier - a unit that is used to determine the thickness of fabric. 

This makes them equals in the big picture, when you get to the nitty gritty, the Fortius Air consists of 16% elastane, whereas Atom LT is equipped with 6% of it. 

I don't have any evidence to prove this, so this isn't scientific, but from what I can see, this more of this fiber tend to make the fabric membrane more durable to inclement weather and abrasion. 

So, 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. It can hug a rock all day and capable of resisting foul weather more than the Atom LT. 

Also, both jackets are DWR applied. 

But using more of elastane doesn't only make the fabric more durable... 

...it also makes it more breathable. At the same time. 

Breathability

Sure, Proton LT's membrane is more breathable than the Atom LT's, but how does that play out in practice? 

Well, even though technology has gone a long way in terms of engineering more breathable and durable fabric, more than half of all the breathability we get under a fabric still results from mechanical venting.

Think pit zips, two way front zippers or, in our case, side fleece panels. This makes Atom LT more breathable than the Proton LT. 

Links:

• https://arcteryx.com/us/en/shop/mens/proton-lt-hoody
• https://arcteryx.com/us/en/shop/mens/atom-lt-hoody
• https://arcteryx.com/us/en/shop/womens/proton-hoody
• https://arcteryx.com/us/en/shop/womens/atom-hoody
• See the side by side comparison of Proton LT vs Atom LT: https://arcteryx.com/us/en/compare/X000004842-distortion/X000005160-oracle

Packability

Neither of these jackets have a pocket that they can stuff into. 

Layering

It's very popular to layer Atom LT and Proton LT with Beta LT, AR or SV. 

If you want to read more about them simply visit their reviews. 

Both jackets are true to size, by the way. So I wouldn't recommend sizing up or down. 

Atom LT 2020 Revision

Not much has changed 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

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. 

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.

Results

Compared to the previous model, the most recent (2019) version of Proton LT is;

• lighter, 
• more packable,
• more breathable,
• slightly less durable.

Fit remains the same. 

Conclusion

These hoodies are much more similar than they're different. Get the Atom LT if you want slightly higher breathability, and get the Proton LT if you want slightly higher warmth, durability and weather & abrasion resistance. 

Links:

• https://arcteryx.com/us/en/shop/mens/proton-lt-hoody
• https://arcteryx.com/us/en/shop/mens/atom-lt-hoody
• https://arcteryx.com/us/en/shop/womens/proton-hoody
• https://arcteryx.com/us/en/shop/womens/atom-hoody
• See the side by side comparison of Proton LT vs Atom LT: https://arcteryx.com/us/en/compare/X000004842-distortion/X000005160-oracle

If you prefer videos, here's a good review of Atom LT:

That of Proton LT:

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.