Arcteryx's Thorium AR and Cerium LT are their second and third warmest down jackets coming right after the warmest down jacket Cerium SV [Read Review] (excluding parkas here).
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).
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: -8 deg C (17 deg F)
- Thorium AR: -14 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.
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).
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 is (you guessed that right) the added weight.
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.
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: -8 deg C (17 deg F)
- Thorium AR: -14 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 an 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 if only it could stand against colder days {below -8 deg C (17 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.
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 -8 deg C (17 deg F)?
- Yes: Get the Thorium AR. I'd recommend the one with the hoody.
- THORIUM AR HOODY MEN'S - Arc’teryx designs for...
- ARC'ESSENTIALS - Versatile high performance...
- DOWN - Highly efficient natural insulation that...
- THORIUM - Versatile down insulated mid layers that...
- ALL ROUND - High performance weather protection...
- THORIUM AR JACKET MEN'S - Arc’teryx designs for...
- ARC'ESSENTIALS - Versatile high performance...
- DOWN - Highly efficient natural insulation that...
- THORIUM - Versatile down insulated mid layers that...
- ALL ROUND - High performance weather protection...
- No: Get the Cerium LT. I'd recommend the one with the hoody.
- CERIUM LT HOODY - Streamlined in its design, and...
- ARC'ESSENTIALS - Versatile high performance...
- CERIUM - Streamlined, minimalist and lightweight...
- DOWN - Highly efficient natural insulation that...
- LIGHTWEIGHT - High performance, minimalist design...
- CERIUM LT JACKET MEN'S - Worn as a mid layer or...
- ARC'ESSENTIALS - Versatile high performance...
- CERIUM - Streamlined, minimalist and lightweight...
- DOWN - Highly efficient natural insulation that...
- LIGHTWEIGHT - High performance, minimalist design...
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 review was helpful for you to understand which jacket would be the best choice for your needs. Feel free to ask me any questions, provide feedback and I'll be happy to respond in the comment section below if it's within my knowledge.
If you couldn't find what you're looking for here, then you can check out my other related posts below.
Best Down Jackets of 2019-2020
Thanks a lot for reading. Happy trails.
References & Further reading
- https://outdoorcrunch.com/arcteryx-alpha-vs-beta/
- https://outdoorcrunch.com/nemo-riff-vs-disco/
- https://outdoorcrunch.com/nano-puff-vs-micro-puff/
- https://outdoorcrunch.com/nano-air-vs-nano-puff/
- https://outdoorcrunch.com/atom-ar-vs-atom-lt/
- https://outdoorcrunch.com/synthetic-insulated-jackets/
- https://outdoorcrunch.com/nano-air-2019-update/
- https://outdoorcrunch.com/nano-air-vs-atom-lt/
- https://outdoorcrunch.com/cerium-lt-vs-atom-lt/
- https://outdoorcrunch.com/cerium-lt-vs-sl-vs-sv/
- https://outdoorcrunch.com/thorsen-therme-camosun/
- https://outdoorcrunch.com/goretex/
- https://triplefatgoose.com/blogs/down-time/a-guide-to-down-jacket-warmth-down-fill-power-vs-down-weight
- https://www.youtube.com/watch?v=KxcmbYq_DRQ
- https://www.youtube.com/watch?v=zwTKytqrPO8
- https://www.reddit.com/r/arcteryx/comments/d0guoo/insulated_jackets_sorted_by_warmth/
- https://en.wikipedia.org/wiki/EN_13537
- https://www.webtogs.com/en-UK/blog/guide-to-down-fill-power-ratings/
- https://en.wikipedia.org/wiki/Fill_power
- https://arcteryx.com/us/en/compare/18013-proteus/21794-orion
- https://www.arcteryx.com/us/en/shop/mens/proton-lt-hoody
- https://www.arcteryx.com/us/en/shop/mens/atom-lt-hoody
- https://www.arcteryx.com/us/en/shop/mens/cerium-lt-hoody
- https://www.arcteryx.com/us/en/shop/mens/atom-ar-hoody
- https://www.arcteryx.com/us/en/shop/mens/thorium-ar-hoody
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