Arc’teryx Cerium LT vs Thorium AR

In FW23, new models Thorium Hoody, Thorium Parka and Cerium Hoody have dropped. However, the older models, Cerium LT and Thorium AR, are still members of the line-up. Arc'teryx told me that they don't know if they will be discontinued in the future or not. 

Links: 

• https://arcteryx.com/us/en/shop/mens/thorium-ar-hoody
• https://arcteryx.com/us/en/shop/mens/cerium-lt-hoody
• https://arcteryx.com/us/en/shop/womens/thorium-ar-hoody
• https://arcteryx.com/us/en/shop/womens/cerium-hoody
• Thorium AR vs Cerium LT side by side comparison chart on arcteryx.com: https://arcteryx.com/us/en/compare/X000006972-24k%20black/X000007131-dark%20elysium

So I visited Iceland a few months ago, and I took my Nuclei FL and Thorium AR there. I kept picking Nuclei FL over Thorium AR pretty often, even though it's much, much less warm. 

The reason for this was precipitation. Thorium AR (and Cerium LT for that matter) is a down jacket, meaning that it loses its insulating power when it gets wet. It also gets soaked in water pretty easily and quickly. 

So, if you're planning to use these jackets in dry and cold areas, then great, keep reading. But for damp areas, I wouldn't recommend these jackets at all - at least not without wearing any shell over it. 

In short, Thorium AR (Men's - Women's) is much warmer than the Cerium LT (Men's - Women's). Cerium LT, on the other hand, is much more packable than the Thorium AR and fits trimmer. These are pretty much their only differences. 

I think Thorium AR will mostly suit better to an average user. 

Raw Name	Arc'teryx Thorium	Arc'teryx Thorium AR	Arc'teryx Cerium	Arc'teryx Cerium LT
Name	Arc'teryx Thorium (Men's - Women's)	Arc'teryx Thorium AR (Men's - Women's)	Arc'teryx Cerium (Men's - Women's)	Arc'teryx Cerium LT (Men's - Women's)
Image
Temp (°F / °C)	7/-14	8/-13	26/-3	28/-2
Breathability	6/10	6/10	Testing	6/10
Weather Resistance	8/10	8/10	Testing	7/10
Durability	8/10	8/10	Testing	7/10
Packability	8/10	8/10	Testing	8/10
Best pick for		Down jacket.
Review	Review	Review		Review
Pit venting?	No	No	No	No
Stuffs into itself?	Yes	Yes	Yes	Yes
Two way zipper?	Yes	No	No	No
Size Chart	[Men's]	[Men's / Women's]		[Men's / Women's]
Type	Down	Down	Down	Down
Fill Power	750	750	850	850
Fill Weight (grams)	140	130	113	102
FP x FW	105,000	97,500	96,050	86,700
Synthetic Insulator (SI)	Coreloft	Coreloft	Coreloft	Coreloft
SI Amount	80 + 140 g/m²	80 + 140 g/m²	80 + 100 g/m²	80 + 100 g/m²
Face Fabric	Arato 30	Arato 30	Arato 15	Arato 10
Activity	All Round	All Round	All Round	All Round
Fit	Regular	Regular	Trim	Trim
Weight	517 g / 1 lb 2.2 oz	490 g / 1 lb 1.3 oz	335 g / 11.8 oz	305 g / 10.8 oz
Length (CB)	71.5 cm / 28.1 in	72 cm / 28.3 in	?	72 cm / 28.3 in
arc-mens-url	https://arcteryx.com/us/en/shop/mens/thorium-hoody	https://www.arcteryx.com/us/en/shop/mens/thorium-ar-hoody	https://arcteryx.com/us/en/shop/mens/cerium-hoody	https://www.arcteryx.com/us/en/shop/mens/cerium-lt-hoody
arc-womens-url	https://arcteryx.com/us/en/shop/womens/thorium-hoody	https://www.arcteryx.com/us/en/shop/womens/thorium-ar-hoody	https://arcteryx.com/us/en/shop/womens/cerium-hoody	https://www.arcteryx.com/us/en/shop/womens/cerium-hoody
pat-mens-url
pat-womens-url
rei-mens-url	https://www.rei.com/product/209333/arcteryx-thorium-down-hoodie-mens	https://www.rei.com/product/135330		https://www.rei.com/product/117169
rei-womens-url		https://www.rei.com/product/134095		https://www.rei.com/product/152545
backcountry-mens-url
backcountry-womens-url
amazon-mens-url		https://www.amazon.com/Arcteryx-Thorium-AR-Hoodie/dp/B09CDMRF5J		https://www.amazon.com/Arcteryx-Cerium-Hoody-Lightweight-Conditions/dp/B0973K9G2H
amazon-womens-url		https://www.amazon.com/Arcteryx-Thorium-AR-Hoody-Chandra/dp/B0163RBV60		https://www.amazon.com/Arcteryx-Cerium-Womens-Lightweight-Conditions/dp/B09QLH2D5V
image-url	https://images.arcteryx.com/F22/1350x1710/Thorium-Hoody-Forage.jpg	https://images.arcteryx.com/F21/1350x1710/Thorium-AR-Hoody-Figment.jpg	https://images.arcteryx.com/F22/1350x1710/Cerium-Hoody-Habitat.jpg	https://images.arcteryx.com/F21/1350x1710/Cerium-LT-Hoody-(NAM)-Distortion.jpg

I'd recommend you to check out their warmth ratings below and make your purchase accordingly: 

Try out the jacket finder tool at arcteryx.com too. 

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). 

You can see this in Arc'teryx's Naming Scheme Page here as well - for both "LT" and "AR", as well as "Cerium" and "Thorium". 

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

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.

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?

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 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. 

Links: 

• https://arcteryx.com/us/en/shop/mens/thorium-ar-hoody
• https://arcteryx.com/us/en/shop/mens/cerium-lt-hoody
• https://arcteryx.com/us/en/shop/womens/thorium-ar-hoody
• https://arcteryx.com/us/en/shop/womens/cerium-hoody
• Thorium AR vs Cerium LT side by side comparison chart on arcteryx.com: https://arcteryx.com/us/en/compare/X000006972-24k%20black/X000007131-dark%20elysium

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.