So why not make an entire post about it?
The main difference between these jackets is that Atom LT uses a synthetic insulation (designed for active use) whereas Cerium LT uses down insulation (and little synthetic insulation in addition to down - designed for low activity use).
You can see this in Arc'teryx's Naming Scheme Guide here as well - for both for "Cerium" and "Atom", as well as the meaning of modifier "LT".
How does this difference is reflected when wearing these jackets?
Cerium LT is noticeably warmer (although not too much) in dry conditions (important).
It also takes a long time to dry, which is another downside.
Another thing to consider is that it takes longer for your body to warm up a down jacket (Cerium LT) compared to a synthetic jacket (Atom LT). You don’t get that instant warm effect with down.
°F / °C
Arc'teryx LEAF Cold WX Parka SVX (Men's)
Arc'teryx Ceres SV (Men's)
Arc'teryx Dually Belay Parka (Men's)
Arc'teryx Thorsen Parka (Men's)
Arc'teryx Centrale (Women's)
Arc'teryx Therme Parka (Men's)
Arc'teryx Camosun Parka (Men's)
Arc'teryx Patera Parka (Women's)
Arc'teryx Kappa (Men's)
Patagonia Vosque 3-in-1 Parka (Women's)
Arc'teryx Magnus Coat (Men's)
Read more about this chart here in my Insulated Outerwear Temperature Ratings Guide.
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.
If you think you run warmer or colder than the average person, then shift temperature ranges accordingly.
If you're interested in down jackets only, see my Best Down Jackets post.
The main downside of synthetic insulation, on the other hand, is that it requires more insulation to provide the same warmth of down - hence ultimately making the jacket heavier than down jackets.
That's why, in our case, Atom LT is 100 grams (4 oz) heavier than Cerium LT (415 g (14.6 oz) vs 305 g (10.8 oz)) - and despite this extra weight, in dry conditions, Atom LT STILL can't provide the warmth the Cerium LT does.
In wet conditions, though; that's another story (more on this a little bit later).
A second downside synthetic insulated jackets have over down jackets is that it'll also lose more insulating power with time - whereas down insulation can provide the same warmth for decades.
These are the essential differences you should know about these jacket types.
Before I get to their ultimate warmth ratings...
Last thing I want to do is to confuse you even further...
I also want you to consider Proton LT as well.
You can think of it as in the same design line with the Atom LT - but a superior version of it. You can read more about their background history, all the differences between them as well as Arc'teryx's motivation to release the Proton LT here.
Click here to see the side by side spec comparisons of all 3 of these jackets on Arc'teryx's own site.
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 where an average person can wear these jackets without feeling cold can be listed as:
- Cerium LT: -8 deg C (17 deg F)
- Atom LT: 0 deg C (30 deg F)
- Proton LT: +3 deg C (37 deg F)
If you think you run hotter or colder than the average person, mentally shift these temperatures accordingly.
When/if it's fairly wet out, Cerium LT's warmth will drop significantly and will end up around Atom and Proton LT's warmth range depending how wet it gets.
Atom and Proton lines are designed as active insulation pieces.
Atom LT's side fleece panels and Proton LT's highly breathable advanced insulation will breath much more than the Cerium LT, and ultimately end up preventing you from overheating.
Cerium LT is designed as a mid-layer to be worn under a shell. Breathing will significantly suffer with the Cerium LT. You wouldn't want to be wearing Cerium LT when, for example, climbing or skiing.
This isn't necessarily a bad thing (depending on your use), but absolutely something important to consider.
All these jackets come with the identical, trim fit.
Face Fabric Differences
This is the biggest downside of not only the LT - but also the other two (SV and SL) models of Cerium.
Since it isn't meant to be worn as a stand-alone piece when it's wet or harsh out, the face fabric is just too fragile. It isn't abrasion resistant. Not wind or weather proof either.
Proton LT and Atom LT, on the other hand, is much better compared to the Cerium LT in this department - although still not as good as Atom AR, Patagonia Nano Puff or Patagonia Micro Puff.
All 3 of these jackets are also DWR coated.
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.
Although this helps Cerium with its water resistance, it just isn't nearly enough take it to Atom and Proton's level.
So what does all this tell us?
If you'll be physically active, then don't get Cerium LT. Simple as that. As explained repeatedly in this post, it just really isn't designed for high output use. Get Atom LT or Proton LT instead. You can check out my Atom LT vs Proton LT post if you can't decide which one to go for.
If, on the other hand, you'll mostly be using the jacket in the neighborhood, then read on...
If you will be wearing an outer layer on top of these jackets...
Do consider the things I mentioned above, but in this case Atom LT and Proton LT lose most (if not all) the advantages they have over the Cerium LT.
You're highly likely to be better getting a Cerium LT. Here are the models with and without the hoody if that's you:
I'd recommend the one with the hoody.
If you now think that you might want to invest in a hard shell outer layer, checking out this post of mine can be helpful.
If you won't be wearing an outer layer on top of these jackets...
Then I'd make up my mind according to this question:
How will the weather mostly be challenging you?
- Precipitation? Then get the Atom LT or Proton LT (again, models with the hoody are recommended):
- Cold (fair amount of days under 0 deg C (30 deg F))? Then get the Cerium LT.
If it's BOTH cold and precipitation that will be challenging you, then sorry but none of these jackets would cut it for you.
In that case I'd recommend you to consider getting an Atom AR - which you can read more about here in my post. Although Atom AR won't be MUCH warmer than the Cerium LT in dry conditions, in wet conditions the difference will be day and night - you'll feel much warmer inside the Atom AR compared to Cerium LT.
Here's the Atom AR if that's you: