There are durable garments, there are breathable garments, and there are relatively few garments that are both durable and breathable. Part of the difficulty with designing something that meets both of those specifications is just that making things breathable often means making them lighter, and that’s bad for durability. However, with the re-design of their well-known Proton LT Hoody, Arc’teryx is shooting for the ultimate durable, breathable mid layer. This piece really caught me by surprise, so I’m breaking out of my normal product break-down and instead sharing a story about this piece and will follow it with some more technical commentary.

Arc’Teryx Proton LT Hoody Features:

  • Air permeable Coreloft™ Compact 80 insulation regulates a comfortable micro climate
  • Fortius™ Air 20 face fabric effectively balances air permeability and weather resistance with lightweight durability
  • Coreloft™ Compact 60 insulated helmet compatible hood gives additional warmth
  • No Slip Zip™ front zipper
  • Dual back flaps on main zipper prevent wind penetration
  • Insulated hood
  • Adjustable hood drawcords
  • Helmet compatible
  • Claimed weight for a medium: 13.2oz
  • MSRP: $299
Arc'teryx Proton LT Hoody Review

All smiles in the Proton

I’m changing my mind about active insulators

So I have to be honest, I am pretty skeptical about the claims made about active insulator jackets. The whole premise here is that you should be able to keep them on all day because of how breathable they are, and any heat you generate will be efficiently regulated to keep you warm without overheating. But I am one of those outdoorsmen who just run super, super hot. I heat up quickly, I stay warm, and I sweat. A lot.

With that, I have tested a few different active insulators over the years looking for the one that would live up to its claims. In a lot of ways, I haven’t really found that. Most of the pieces I’ve tested have been pretty top-notch, with premium fabrics and expert design and manufacturing. But they have still wound up feeling heavy, or too warm, or like they saturate with sweat. As a result, I’ve been a bit shy to take active insulators on trips as a key layer – that is, one that I actually rely on rather than taking as an extra.

Arc'teryx Proton LT Hoody Review

Chest pocket keeps organization simple

Fast forward to this January, when I took a five-day hut trip with friends in British Columbia, Canada. It was incredible skiing with big backcountry days and tons of fun terrain. The weather was really challenging, too, with storms dumping 2.5 feet of snow during our stay with substantial wind effects. Since we were in a hut, I carried up some extra goodies like more food and drinks and – in the bottom of my pack – the tester jacket from Arc’teryx that I knew I needed to try out.

The trip progressed and we had day after day of great skiing, but the Proton LT stayed at home as I relied on other layering strategies that had served me well in the past. I tended to go with systems that incorporated a larger number of layers to accomplish the task: a baselayer, a fleece, and then a shell for the uphill with a puffy in my pack for the ridgetop transitions and descents.

Arc'teryx Proton LT Hoody Review

Just enjoying some Canada pow near dusk.

That system was working perfectly fine, although the transitions were definitely uncomfortable with the cold biting wind as I switched layers. I also felt like my shell trapped in lots of heat, even when I had the main zip down and the pit zips open.

By the last two days, I knew I needed to get the Proton LT out for some tests because I am, after all, a gear tester. So, on a windy, blustery January day in Canada, I stepped out of the cabin wearing just my base layer and the Proton LT to see how I would fare in the harsh cold world. It was a really cold day on the skin track, with blowing wind and snow.

My initial impressions of the piece were mostly about how comfortable it was: the Proton LT is tailored impeccably well, not too athletic as to be tight but trim enough to feel fast and lithe. My size L fit my 5’11”, 195-pound body perfectly. The cuffs on the sleeves feel luxurious against your hands, and the high collar gives a sense of invulnerability from the biting wind. My body warmed up quickly, but it felt well balanced by the amount of heat that the wind was stealing away from the jacket.

As we left the relatively flat road and started gaining a ridgeline, the jacket really came into its own. As I got substantially hotter and started to sweat, the jacket whisked away sweat and never became saturated, even in high-moisture areas like my underarms and forearms. We climbed for a good 75 minutes before resting and I was putting out plenty of heat, but opening the main zip was all I needed to do to equilibrate. The DWR was more than adequate to fend off the falling flakes that accumulated on the inside of my elbows. Overall, it was easier (and more comfortable) than my previous system of a base/fleece/shell.

I repeated this the next day with similar results, and I’ve continued to wear it on cold touring days. I’ve tested some incredible active insulators before, but this is the first one that I have truly kept on ‘all day’ as promised by the advertising hype.

Arc'teryx Proton LT Hoody Review

The Proton LT made a great touring companion on rough weather days

The nitty gritty behind the Arc’teryx Proton LT

There are a couple of reasons behind why I wound up liking the Proton LT so much. One of the first ones, to be honest, is choosing good days to use it on. For me, I know it needs to be a pretty cold day. It also helps if it’s a bit windy, which seems to keep the jacket just right for me. Humid, warmer days are a recipe for failure for me and active insulators. Beyond that, though, there are some particular traits of the Proton LT that I want to highlight.

The fundamental thing is the proprietary fabric that Arc’teryx built the Proton LT out of. The main insulation is their Coreloft 80 body insulation, wrapped inside their Fortius Air 20 fabric. Translated out of their somewhat cryptic names, what this means that the Coreloft is an 80 gram per square inch weight, and the Fortius Air face fabric is 20 denier. Focusing on the Coreloft weight, that puts it at an interesting place between two other top-notch active insulators I’ve tested. The Rab Alpha Direct jacket is 120g/in and the Westcomb Tango is the 60gm/in. Both of these are done with Polartec Alpha, which frankly I would expect to breathe better than Coreloft due to its impressive R&D history with roots in military applications.

Comparing these three jackets, I find that the Rab Alpha Direct’s 120g/in weight is just too heavy for me to be active in. I simply can’t move uphill in it unless temperatures are in single digits, otherwise I overheat. By contrast, the Westcomb piece (which is made in Canada and is quite premium) is aided by its lighter insulation but hamstrung by a poor design of the forearms, which start to feel heavy and clingy as you get hot and start to sweat. Additionally, the main body does feel susceptible to some more wind penetration that whisks away your body heat.

Arc'teryx Proton LT Hoody Review

Charging uphill doesn’t really phase the Proton LT

By contrast, the Proton LT shines in comparison to these (frankly quite stellar) competitors. The 80g/in insulation seems like the perfect balance to me, warm enough to fend off winter temperatures and windier days, without feeling heavy or oppressive at all. This is aided somewhat by the zoned 60g/in insulation on the hood, which reduces overall weight and bulk. It’s aided even more by the Fortius 20 face fabric, which is a change with the redesign which is more durable than the original but is wonderfully air permeable. This is especially noticeable on windy days, as there is still some wind penetration into the jacket.

Working together, the Coreloft and Fortius fabrics do an excellent job regulating the microclimate in your jacket. They are also lightweight and packable, although the jacket does not have a pocket that it can pack into. That’s fine with me, as tight compression breaks down synthetic insulations quickly.

Other than that, the jacket has a great feature set. The main zipper doesn’t creep down; the single chest pocket is roomy and can accommodate bars, radios or whatever you need. The two zippered hand pockets are also quite spacious and are nice for warming up.

Crucially, the hood has Arc’teryx’s Halo adjustment, so it’s easy to get a good fit around your head that doesn’t obscure your vision. It’s also helmet compatible. The buttery-soft cuffs are a nice touch, and the hem has an adjustment as you’d expect.

Arc'teryx Proton LT Hoody Review

Simple hem adjustment is effective to hold things in place

The Good:

  • Fabrics work well together to create an equilibrated microclimate between you and the jacket
  • The fit and tailoring of the jacket is flawless for my taste
  • You can keep the jacket on all day as promised, unless it’s too warm for insulation
  • The no-slip zip slides easily and stays where you want it
  • The tall collar adds comfort and protection
  • The hood stays where you want it to thanks to the single adjustment

The Bad:

  • It’s an expensive piece at $300
  • Despite my success with the piece, others may find it too warm or too cold

The Bottom Line: Arc’teryx Proton LT Hoody

This was a long review, but I wanted to communicate that I’ve tested some great active insulators in the past and this was the first one that lived up to the hype. Since those first days in Canada, the Proton LT has continued to be my go-to piece for ski touring on sufficiently cold days. I also wear it all the time around town because it’s so comfortable. It’s easy to recommend this piece for high-output backcountry adventurers.

Buy Now: Available from

About Author

Kevin Glover is an outdoorsman living, climbing and biking in Spokane, WA. Originally from the Nevada high desert, he moved to the PNW for its mild winters and allergen-free summers. He has guided throughout the Cascades and Enchantments for Peak 7 Adventures.


  1. geoffrey swindler on

    I’m going into the Brooks Range next August for 10 days. I’m expecting temps from 50-70 during the day with rain likely a few days. I ave the Proton LT and the Rab Alpha Direct. Given the likely rain, which jacket would you suggest? Thanks. Geoff

    • It’s a good question. For me, I’d get too hot in either one of them in those temps but I tend to run hot overall. With that, I might lean towards the Rab just because it breathes a bit better thanks to the exposed insulation fibers.

      Thanks for asking!

  2. Great article. Is this the “Neptune” color? REI has a color called “Neptune/Orion” in the REI-garage, but I can’t figure out what it looks like. The site seems to show it in Labyrinth.

    • Yep you’ve got it, it’s the Neptune colorway. It’s a season old so there’s a good chance the Garage has what you’re looking for since this year’s lineup doesn’t have that color.

  3. Terrific review, Kevin! I’ve owned and used a Proton LT for two years now …. hiking, mountain-biking, other high exertion level stuff …. here in the Colorado Front Range and simply love it. I’m skinny and need insulation; but the type that accommodates high exertion efforts … and the proton LT does just that. Highly recommend!!

    One nit: the Coreloft is 80 grams per sq. yard/meter, not per square inch I believe.

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