Arc'teryx Atom LT jacket - a lightweight best worn on the go Review

© Dave Saunders

Since there are so many synthetic insulated jackets on the market, you really need to ask yourself what you're looking for in terms of end use. If you're going down the lightweight route, for instance, then there will inevitably be tradeoffs. Arc'teryx's Atom LT ('light') is a lighter version of the Atom AR ('all round'), and it definitely hits that lightweight remit. As a result it's really not that warm: arguably, its strength is its breathability when worn on the go. Arc'teryx products fall at the upper end of the price spectrum - so what do you get for the extra bucks, and what compromises come with the Atom LT's lightness?

It's light and breathable, but not very wind resistant  © Dave Saunders
It's light and breathable, but not very wind resistant
© Dave Saunders

The recent lockdown made gear reviewing a little challenging, however our mini 'beast from the east' allowed a proper test of the Arc'teryx Atom LT jacket in a variety of wintry situations that UKH/UKC people might find themselves in. I used this synthetic lightweight insulated jacket throughout the winter while hillwalking, winter climbing, nordic skiing and as a light-but-warm extra emergency layer in my bag when out hill running. It's light enough to stay in the pack for spring and even summer use, and it ought to appeal to weight conscious folk such as backpackers and summer alpine climbers.

A versatile top that works as midlayer or outer  © Dave Saunders
A versatile top that works as midlayer or outer
© Dave Saunders

Local winter scratching in the mini beast from the east  © Dave Saunders
Local winter scratching in the mini beast from the east
© Dave Saunders

In winter - mostly a midlayer 

I have used the Atom LT as an outer during climbing, walking and nordic skiing in more benign winter weather. It feels light and unencumbered in the upper body, and breathable enough that you can wear it in comfort when working hard. However, with this breathability comes air permeability, and you feel cold penetrating when the wind blows hard. For this reason, most of the time in the winter I ended up putting a shell over the top. I'd dispute Arc'teryx's claim that this jacket has "a high degree of weather resistance" - that's not what it's for at all.

Lightweight stuff like this could be used all year round in various environments. In less challenging conditions it'll function as an outer layer, but for winter in particular this really feels predominantly like a midlayer, and much more an active piece than something to stand around in for hours. Just to be clear, this is not in any way in belay jacket territory - at least not as far as winter is concerned.

Fit and cut

The Atom LT comes in both men's and women's versions. At about 5'11'' and roughly 75kg (to mix my measures) I've been using a men's size Medium. I have been wearing this over a warm baselayer and occasionally a thin fleece hoody as well. I'm pretty slim but even on me there is not masses of room to add more substantial layers without feeling restricted. The stretch panels at the sides mean you can achieve quite a close fit although the lightness of the structure means it does flap about at times when you are wearing this as an outer. I have been wearing an athletic fit type Gore Tex shell (Salewa Ortles 3) over this a lot of the time. The Atom does at times poke out of the bottom of this, so it is cut quite long which on balance is a good thing in terms of keeping the midriff warm and draught-free. Being too short in the body is a common review criticism of garments like this, so it's nice to see a bit hem length here.

I have sometimes noticed a tendency for the jacket to ride up under a rucksack hip belt - however that effect may have been peculiar to the arm action of using long poles during Nordic skiing, because it doesn't always happen.

When the jacket is hung up or in a pile it looks rather insubstantial, but when you put it on it seems to have more of the feel of a fluffed up insulated jacket! When the jacket is zipped up it comes up nice and high around the neck, which makes it feel cosy and I guess this helps squeeze the most warmth out of the minimalist design.

The Atom LT has a good active fit for climbing  © Dave Saunders
The Atom LT has a good active fit for climbing
© Dave Saunders

Breathable enough for active use, such as nordic skiing  © Dave Saunders
Breathable enough for active use, such as nordic skiing
© Dave Saunders

Stripped-back features

This is out and out lightweight, so one should not expect masses of features. There are two external zipped pockets suitable as hand warmers as they go inside the layer of insulation. Unfortunately neither of these functions as a stow pocket, which is a feature that would have made sense in a lightweight jacket that you might want to stuff down as compact as possible in a pack, or hang off your harness on multi pitch routes. There is one internal chest pocket which is relatively large. The cuffs are not adjustable, just simple stretch fabric. The hem has an elasticated drawcord; that's about it, the architecture of the jacket is mostly a vessel for the insulation.


The rear of the hood has a volume adjuster toggle; the elastic tracks the lower edge of any hat you are wearing so it feels quite secure. The rim of the hood is not adjustable, is not wired and it does not have any kind of peak although there is a short length of stiffening above the eyebrows. The hood is cut in a way that it will fit under a helmet, however I was quite surprised to find that it did go over a helmet well enough to offer some benefit, too - but it is not what you would categorise as helmet compatible.

The hood has a nice snug fit on a helmet-less head  © Dave Saunders
The hood has a nice snug fit on a helmet-less head
© Dave Saunders

The hem doesn't always seem to want to stay down
© Dave Saunders

Outer fabric

The outer fabric is Tyono™ 20 which seems hyper-breathable and has a ripstop-type grid to increase durability; however, the fabric does feel extremely thin and is quite noisy. It may be worth noting the voices on the UKC/UKH gear forum which have raised concerns about how robust this fabric may be - see here.

On this hybrid jacket the side panels are different, and instead of a 3-layer outer insulation and inner fabric, they are a single layer brushed microfleece with a smooth outer surface the same colour as the rest of the jacket. These stretchy side panels aid breathability and movement. So far, it is actually this material which has shown signs of wear on my jacket, as it has gone bobbly in places; other than this there are no other obvious signs of wear and tear during the test period.

Its DWR treatment helps the jacket shrug off light showers, but one issue discussed more below is that the outer is so thin that when it does get wet it really does feel wet through.

Testing its DWR in the rainy Lammermuirs  © Dave Saunders
Testing its DWR in the rainy Lammermuirs
© Dave Saunders


The Atom LT uses synthetic polyester Coreloft Compact insulation, which is made to maximise lightness and compressibility. At a weight of 60g/m2, there's not a huge amount of fill, but it seems well judged for the jacket's remit. Coreloft is composed of mixed diameter fibres, the larger diameter ones are to maintain loft, and the manufacturers claim these allow lighter weight face fabrics to be used as a consequence. The Atom LT does feel reasonably warm for its weight.

This hi-tech insulation does not actually provide full coverage as there are some stretch panels at the sides from hip to armpit. If you unfold the jacket you can see that around two thirds of the area of the whole torso is covered with a three layer sandwich of Coreloft. The remaining third is that single layer of thin microfleece with some kind of bonded face material; this seems to take up quite a lot of the area protecting the torso, and given its relative wind-permeability it does make me wonder what the thermal impact of that might be.

As an end user it is difficult to say from use how Coreloft Compact compares with other synthetic insulation such as Primaloft. However, by comparison I would say the Atom LT is not as warm as my Alpkit Katabatic (Primaloft) jacket - but then that is also a slightly heavier jacket overall. 

Any insulation can become wet from sweat, especially if a shell is worn over the top. This is because the water vapour condenses out as it enters the cooler outer layers of clothing. Arc'teryx are careful to point out that the 'warm when wet' rule applies to this garment and its insulation. However what I did notice in winter is that the Atom LT has a tendency to feel soaking wet during brisk activity when worn under a shell. It was probably no wetter than other garments would have got, however the lightness of the face fabric seemed to emphasise this effect; a comparison with wet tissue paper is probably a bit harsh, but you get the idea.

Conversely, hyper-breathable jackets like this do seem to dry out quite quickly when they form the outer clothing layer; I've been aware the moisture issues seem to disappear when I'm able to remove the shell outer. I would agree with Arc'teryx that it does have a fast dry time.

The high collar is nice and snug
© Dave Saunders


None of us want to carry excess weight for the sake of it, but in the case of insulated jackets it's worth asking how far you can go in terms of weight reduction before you start to compromise warmth, durability or other features you may require. While you can get lighter still (the Rab Xenon for instance), the Atom LT can definitely be classed as a lightweight. To take another example, it comes in around 10% lighter than a light-ish synthetic jacket I previously reviewed, the Alpkit Katabatic. But it compromises on insulating performance in order to get there, and although I'd say the Atom LT feels warm for its weight, I do not think it is as warm as my slightly heavier random alternative example.

While it'll work as a stand-alone jacket in spring and summer, for colder conditions it's best considered a midlayer. Thanks both to its lightness and its air permeability, the Atom LT is not something to stand around in for hours, but on the other hand, being so breathable it works very well as 'active insulation' when you're on the go - which is something you can't say about a lot of synthetic insulated jackets. In short, this jacket has both strengths and weaknesses, which are worth bearing in mind when deciding what to pack for the day. 

It is good that Arc'teryx are very open about where this jacket is manufactured and by whom (Youngone (CEPZ) Ltd., Bangladesh). There seem to have been questions raised in connection to this supply chain previously in connection to whether unfair labour practices are occurring. I found that investigating this in detail is not that straightforward. Maybe we should all ask more questions about where our gear comes from?

Arc'teryx say:

Alpine proven as a midlayer and standalone, this versatile hoody has warmed climbers and backcountry travelers for years. Built to handle a range of conditions and output levels, the latest-generation Atom LT's Coreloft™ Compact insulation retains its warmth even if wet and has loft retention to withstand years of packing and unpacking. The water resistant Tyono™ 20 face fabric is breathable and durable, stretch side panels improve fit and freedom, and the insulated StormHood™ adds warmth.

  • Sizes: XS-XXXL (men) XS-XXL (women)
  • Weight: 375g (men) 320g (women) - brand's weights 
  • Versatile synthetic insulated mid layers with a high degree of weather resistance
  • High performance, minimalist design that is durable for its weight
  • Versatile high performance designs for diverse activities and conditions
  • Man-made insulation with quick dry times, durability and retains warmth when damp
  • Adding pigment at the polymer level which saves water, reduces C02 emissions and increases fabric colourfastness
  • Dope Permeair™ 20 - 100% nylon
  • Tyono™ 20 denier shell with DWR treatment - 100% nylon
  • Stretch fleece - 94% polyester, 6% elastane
  • Coreloft™ Compact (60 g/m² ) insulation. Highly crimped, multi-denier siliconized polyester yarn that has undergone a special process which reduces the thickness of the material by 50%, without reducing its insulation value by the same amount. Lightweight, breathable, thermally efficient 100% polyester fibre.

For more info see

Support UKC

As climbers we strive to make UKClimbing the kind of website we would love to visit, with the most up-to-date news, diverse and interesting articles, comprehensive gear reviews, breathtaking photographs and a vast and useful logbook system. As a result, an incredible community has formed around the site - we’ve provided the framework but it’s you who make the website what it is today. If you appreciate the content we offer then you can help us by becoming an official UKC Supporter. This can be a one-off single annual payment or a more substantial payment paid monthly or yearly which includes full access to Rockfax Digital and discounts on Rockfax print publications.

If you appreciate UKClimbing then please help us by becoming a UKC Supporter.

UKC Supporter

  • Support the website we all know and love
  • Access to a year's subscription to Rockfax Digital.
  • Plus 30% off Rockfax guidebooks
  • Plus Show your support UKC porter badge on your profile and forum posts
UKC/UKH/Rockfax logo

Loading Notifications...
Facebook Twitter Copy Email