I'd recommend the Thorium AR (see image) over the Cerium LT to most (maybe all?) of you.
Arcteryx's Thorium AR [Men's - Women's] and Cerium LT [Men's - Women's] are their second and third warmest down jackets, coming right after the warmest down piece Alpha Parka [Men's - Women's] (excluding line 24 here).
Try out the jacket finder tool at arcteryx.com and you'll see this yourself.
Summary
Thorium AR vs Cerium LT comparison should come to your mind only if you're looking for a (1) multi-use jacket to use out in (2) cold and (3) dry weather.
#Note: If this isn't you, stop reading this post right here and go to my Arc'teryx Jackets Guide.
Thorium AR is MUCH warmer and more weather resistant than the Cerium LT. However, it’s also quite a bit heavier {17.3 oz (490 g) vs 10.8 oz (305 g}.
Another important difference is that Cerium LT offers a trim cut, and the Thorium AR a regular cut.
- #A sidenote here: Arcteryx.com's PDF guide to their jackets is GOOOLLDDD. Highly recommend you to check it out before you buy.
Before we begin, let me clear this out of our way. I wouldn't recommend either of these jackets if:
- You'll be wearing them as a stand alone piece when there's either heavy rain, snow or wind a fair amount of days;
- You won't be treating them very kindly and/or its outer shell will be in contact with rough surfaces.
This is all because both jackets have quite fragile face fabric with Thorium AR being a little superior to the Cerium LT (more on this later).
- Some of the Arc pieces you see in this post might be discontinued, and hence might be unavailable at arcteryx.com.
- If that's the case, then I'd recommend you to check out this page at REI. You might be able to find them there.
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 | Review | |||
|---|---|---|---|---|---|---|
| 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.
That said, although they make quite vulnerable outer layers out against these harsh conditions, they are perfect mid-layers. If the above two bullets don't apply to your situation, they'd make perfect stand-alone pieces as well.
Warmth
Point #1) 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, an average person can wear these jackets just comfortably at:
- Cerium LT: -2 deg C (28 deg F)
- Thorium AR: -13 deg C (8 deg F)
If you think you run hotter or colder than the average person, shift these temperatures accordingly.
Point #2) Thorium AR is also baggier - which makes thicker under layers a more proper and comfortable option.
Cerium LT uses a 850 fill power European grey goose down, whereas Thorium AR uses 750.
This value is in cubic inches, and represents the end volume the down eventually fully expands to when it's at rest.
The more the volume, the more air will be > trapped inside the down > heated by your body > and ultimately work as an insulation.
That's why the higher the fill power, the warmer you'll feel inside the jacket provided that both jackets are filled with the same amount down.
What does that mean?
It means that a down jacket with a 750 FP (fill power) down can provide more warmth than a 850 FP down by using more of 750 FP down.
And this is exactly what's happening in our case. Thorium AR provides more warmth than Cerium LT by using this strategy.
- Thorium AR: Equipped with 132 grams (4.65 ounces) of 750 down fill
- Cerium LT: Equipped with 102 grams (3.5 ounces) of 850 down fill
The downside of this (you guessed that right) is the added weight.
850 FP down of Cerium LT also makes it extremely compressible. Its stuff sack size is hence smaller compared to that of Thorium AR (plus point for traveler folks).
That's why, in the end, this trade-off makes Thorium AR nearly 200 grams heavier than Cerium LT {(490 grams (1.1 lbs) vs 305 grams (0.7 lbs)} in return.
But I'd give relatively less importance to this weight difference, because as you can see here on Arc'teryx's own Naming Scheme Page, both Cerium and Thorium lines are on the lighter side.
Results
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: -2 deg C (28 deg F)
- Thorium AR: -13 deg C (8 deg F)
If you think you run hotter or colder than the average person, mentally shift these temperatures accordingly.
Important:
When/if it's fairly wet out, warmth provided by both jackets can and will drop significantly.
One more thing to consider for warmth: Fit
Thorium AR's regular fit is baggier compared to Cerium LT's trim fit.
This doesn't only make under layering easy and sweet, but it also increases warmth even when you wear the same under layer beneath these jackets.
How?
Baggier cut of Thorium AR makes under layering easier.
Due to the baggier cut, there's more air trapped between your body and the jacket, which works as a perfect extra insulation.
Baggier cut doesn't always equal more warmth. There's a fine balance and you can often go too baggy and eventually and let too much air circulate & end up providing even less warmth than with the trimmer case to begin with.
But Thorium AR is at the warmer side of this line and hence provides extra warmth leveraging its baggier cut.
Lastly, both offer the same hem length at 72 cm (28.3 inches).
If you think Cerium LT would really work for you only if it could stand against colder days {below -2 deg C (28 deg F)}, then you might better checking out Cerium SV post of mine.
Cerium SV is warmer than Thorium AR by a good margin - standing up temperatures against as low as -20 deg C (-5 deg F). It's also only 400 grams (15 oz) at total - 100 grams (3.5 oz) lighter than Thorium AR.
Its face fabric, though, is still as fragile as that of the Cerium LT's. Actually, technically speaking, it's even MORE fragile than that - but that's pretty much not noticeable.
Speaking of which... Let's get to weather resistance.
Weather resistance
Cerium LT uses a thinner, lighter fabric on the outer shell (Arato 10) compared to Thorium AR (Arato 30).
This is the biggest downside of not only the LT model but also the other two (SV, SL) Cerium models.
Cerium LT isn't designed to be worn as an outer shell in harsh conditions. It's face is quite fragile - it can even get torn by something what would otherwise be a harmless rub for a rather robust jacket like the Atom AR.
Arato 30 of Thorium AR is absolutely more wind resistant, water resistant and durable than the Cerium LT - but still not nearly as robust jackets like Atom AR or Patagonia's Nano Puff and Micro Puff Jackets. Atom LT and Proton LT are also better than these two in this department.
In dry conditions, Atom AR would be less warm than Thorium AR and more than Cerium LT.
But in wet conditions, being equipped with synthetic insulation rather than down, (also having a super robust outer shell) Atom AR would feel warmer than both of these jackets.
Thorium AR isn't windproof by any means either. It's only lightly wind-resistant.
That said, both are 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.
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.
DWR will be enough to repel some moisture and light rain.
About wearing them as a stand-alone piece, please don't let my language discourage you more than necessary though (especially for the Thorium AR).
As long as you're kind to these jackets and you won't be out in harsh wind and/or rain, you'll be perfectly fine.
If this is you, though, it probably means that you'll be wearing this jacket out in town vast majority of the time, so I'd also recommend you to consider getting either a Thorsen, Camosun or Therme.
If you're looking for a windproof AND down-insulated jacket that you CAN wear as an outer layer as well, then I'd recommend checking out the Ceres SV Parka or the Firebee AR Parka. Cerium SV won't work either.
If a down jacket isn't a must for you, then checking out my top Arc'teryx and Patagonia synthetic insulated jacket picks might help you.
Conclusion
It might sound oversimplified (it is), but it all really mostly comes down to your response to this question:
Will there be a lot of days below -2 deg C (28 deg F)?
- Yes: Get the Thorium AR. I'd recommend the one with the hoody.
- No: Get the Cerium LT. I'd recommend the one with the hoody.
Lastly, both Cerium LT and Thorium AR come with their own stuff sacks (plus points for travelers) with that of LT's being more compact due to higher quality (850 FP vs 750 FP) down fill.
Layering suggestions
I'd recommend layering these jackets with a hard shell. Beta AR [Read Review] would probably work pretty well with both.
A base layer is definitely less necessary than an outer layer, but if you'd like extra insulation, this baselayer of Arc'teryx can work pretty well.
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!
At the beginning of the article you state, “Thorium AR is not only warmer and more weather resistant, but it’s also quite a bit lighter (17.3 oz (490 g) vs 10.8 oz (305 g)) than the Cerium LT”.
In what universe is 17.3 ounces, lighter that 10.8 ounces???
That should read:
Thorium AR Hoody is warmer and more weather resistant, however, it’s also quite a bit heavier at (17.3 oz (490 g) vs 10.8 oz (305 g) than the Cerium LT.
That was a huge mistake. Thank you for pointing that out Sean. Fixed.
I own a Cerium LT jacket for years, loved it! However, there is no way the Cerium LT is capable to keep you warm at -8 C, maybe – 2 to -3 at most to my experience.
Wow thanks for your in depth reviews. I own a car showroom, its gets to about-2 in the winter in the UK with only a small heater. I need a jacket that’s not too heavy as I clean cars and don’t need a hood as I wear my Snowboarding beanie. Which jacket Would you recommend ? I have an unlimited budget for the right jacket. It needs to be warm and versatile and not too long as I’m 5foot 7 and look ok when I’m selling a car and dealing with customers! I have been looking for 3 months and have sent 2 jackets back. Your expert advice would be much appreciated. I was also a ski instructor and have look at every jacket possible, I think! Thanks for your help – Andy – UK
Hello, thank you for your in-depth review. I have one question, upto what + temperature can you wear Cerium LT without feeling too hot (Low activity and with T-shirt on)? . I’m thinking if Cerium LT can also be used in spring as well? Or you’d need Cerium SL for spring? Thanks!
Don’t both the thorium AR and atom AR have the same out fabric? How is one more durable than the other?