Cerium LT vs Thorium AR

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 jacket Cerium SV [Men's - Women's - read my review] (excluding parkas 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 here and go to my Arc'teryx Jackets Guide. 

Thorium AR Hoody is warmer and more weather resistant, however, it’s also quite a bit heavier (17.3 oz (490 g) vs 10.8 oz (305 g) than the Cerium LT. 

Another important difference is that Cerium LT offers a trim cut, and the Thorium AR a regular cut.

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

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: -8 deg C (17 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 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