When deciding between Atom SL and LT synthetic insulated jackets, following chart can be quite helpful for you to make up your mind around it:
I already made a post about Atom AR vs LT, so in this post I'll talk about Atom SL vs LT only.
As you see, in summary, their main differences are:
- Atom LT is A LOT warmer, and also a little bit more comfortable and weather resistant. Designed more for a wide variety of high output activities as well as occasional casual use
- Atom SL is A LOT lighter, and also a little bit more breathable and packable. Designed more for warm weather use in the upper alpines
You can see this in Arc'teryx's Naming Scheme Page here as well - for both "LT" and "SL", as well as "Atom".
It can be a little off topic for you, but I'd also check Proton LT here as well - because it's not only much more weather resistant and comfortable than the Atom LT, but also almost as breathable as the Atom SL and as warm as the Atom LT.
Perfect combination if you ask me. That's why it's my top synthetic insulated jacket, with Atom LT being its top alternative.
The only scenarios I'd recommend the SL over LT would be professional climbing (or alpinism), ultralight summer hiking and/or traveling since SL is more breathable and packable. For all the other folks, (will be out in the town when it's chilly and also during various high output outdoor activities such as climbing, skiing, fat biking, etc.), then my recommendation would be Atom LT - although I'd check out Proton LT as well.
Now let's get to them in detail one by one.
Warmth
There are 4 main things that make Atom LT warmer than the SL:
1) 40 g/m2 (Atom SL) vs 60 g/m2 (Atom LT) insulation density
Coreloft Compact 40 g/m2 of Atom SL is Arc'teryx's lowest density (1.2 oz/yd2) Coreloft insulation.
| °F / °C | Insulation |
|
|---|---|---|---|
Ceres SV (Men's) | -15/-26 | Down | |
-10/-23 | Down | ||
Dually Belay (Men's) | -7/-22 | Synthetic |
|
Thorsen (Men's) | -7/-22 | Down | |
Centrale (Women's) | -5/-20 | Down | |
-5/-20 | Down | ||
Therme (Men's) | -2/-18 | Down | |
Camosun (Men's) | 0/-17 | Down | |
3/-16 | Synthetic |
| |
Patera (Women's) | 5/-15 | Down | |
8/-13 | Down | ||
Kappa (Men's) | 10/-12 | Synthetic |
|
10/-12 | Synthetic | ||
Magnus (Men's) | 14/-10 | Down |
|
17/-8 | Down | ||
23/-5 | Synthetic | ||
24/-4 | Synthetic | ||
28/-2 | Synthetic |
| |
40/5 | Down | ||
48/9 | Synthetic |
| |
50/10 | Synthetic |
Read more about this chart here.
These are only approximate values assuming:
- you only have a long sleeved 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.
Also check out my Arc'teryx Favorites.
If you think you run warmer or colder than the average person, then shift temperature ranges accordingly.
This is also one of the things that make SL exceptionally light - especially compared to the Atom LT {9.2 ounces (260 grams) vs 14.6 ounces (415 grams)}.
Atom LT's Coreloft 60 g/m2, on the other hand, obviously makes it more insulated but also naturally heavier.
2) Atom SL is only core-insulated!
The Atom SL is only insulated in core area of the jacket (kind of like a vest).
The sleeves and hood of the jacket AREN'T INSULATED. They only cut the wind.
Atom LT is much warmer than the SL.
Whereas Atom LT is insulated everywhere.
This also causes a big warmth difference.
3) Coreloft (Atom LT) vs Coreloft Compact (Atom SL)
Besides these differences, another difference here is that SL comes with Coreloft Compact whereas the LT with the basic Coreloft.
Coreloft of Atom LT is more thermally efficient and less air-permeable. Which means that it's warmer but also breathes less.
4) Atom LT is a little baggier than the SL
This helps the LT trap more air between the jacket and your body. That's why, in the end, more air gets heated by your body and works as insulation.​
But the fit difference isn't big, and hence it doesn't cause a big warmth difference.
Combine all these results, and...
I'd say, generally speaking, when it's dry out, with only a long sleeved shirt under and without a shell on top, with a mild wind and very low to no activity level...
The approximate lowest temperatures an average person can wear these jackets without feeling cold would be around:
- Atom SL: 50 deg F (10 deg C)
- Atom LT: 30 deg F (0 deg C)
If you think you run hotter or colder than the average person, then shift these temperatures accordingly.
Atom SL is slightly more breathable than the Atom LT.
Breathability
Now for the 3 main reasons listed under the warmth heading, you'd expect the SL to be breathable, and that's not incorrect, but there's a caveat here.
Unlike Proton LT or Patagonia's Nano Air, Atom line doesn't use highly breathable advanced insulation technology.
Most of its breathability comes from the side fleece panels.
That's why, the insulation differences laid out above actually make up the smaller chunk of this breathability department.
That's why, in the end, SL really IS more breathable, but it's by a much, much smaller amount than it's colder than the LT.
Weather Resistance
Atom SL isn't designed to be waterproof. Its Nu water repellent treatment does a mediocre job at best - can only protect you from very light rain and moisture - nothing more.
LT's DWR coating noticeably does a better job than the SL, but it still isn't anywhere near others such as the Atom AR or even the Proton LT.
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 (Arc'teryx's own product).
I'd recommend both jackets with the hood. SL isn't even available without the hood anyway.
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:
Thank you for reading!
