Arc'teryx Proton LT Hoody Review

© Mike Hutton

The Proton LT is a lightweight synthetic insulated jacket from Arc'teryx. Being very breathable, it's a versatile piece which can be used as a mid-layer as part of a layering system when it's really cold, or as an outer layer when you're more active. In order to give a proper assessment of the Proton LT's capabilities, Theo Moore will be giving his review of the jacket for the kind of cold, damp and windy British winter which lots of us experience, whilst Toby Archer has been putting the jacket through its paces winter mountaineering.

It's a good choice for winter crags and bouldering  © Mike Hutton
It's a good choice for winter crags and bouldering
© Mike Hutton



This jacket is available for both men and women. One of the big selling points of the Proton LT is that it allows you to move freely which is especially important when you're climbing or performing any activity where you regularly lift your arms above your head. The problem which many jackets face when used for these activities is that they restrict the movement of your arms and, when you do lift your arms, the waist rides up leaving your middle exposed to the cold and wind. The Proton LT does very well here - I've found there's no restriction when moving my arms in any direction, and even with the arms raised there's only a slight bit of lift in the hem and, as there's plenty of length in the hem, I find it doesn't lift above the waist. Of course no jacket is going to fit everyone equally well, so it would still pay to try it on before buying, despite my experience.

The Proton LT is cut well for strenuous movement, as you can see here the hem hasn't lifted above the waist  © UKC Gear
The Proton LT is cut well for strenuous movement, as you can see here the hem hasn't lifted above the waist
© UKC Gear

In a men's medium the Proton LT fits me (at 6ft) extremely well. At first acquaintance it's a fairly slim jacket but it is quite stretchy and so can accommodate a base layer and slim fleece underneath it. There's plenty of length in the arms and with elasticated cuffs there's no chance of the sleeves riding up. The elasticated cuffs also work nicely with gloves.


Arc'teryx have cut the Proton very much with climbing in mind, and I agree with Theo - whether bouldering or swinging ice tools, you can reach high with no resistance and little movement at the hem.



The Proton LT is a slim jacket in terms of weight and profile and this also means that, as you would expect, it's slim on features. There's a large outside chest pocket for valuables, two hand pockets and... that's about it. That's certainly not a criticism, as a host of features would only make the jacket bulkier and heavier. It is a bit of a shame that the Proton LT doesn't pack away in to a pocket as it could make a great summer belay jacket. No stuff sack is provided, though you could always use your own.

The cut of the Proton LT does provide two additional features: a lovely high collar which covers your chin and provides extra resistance to the wind, and a very roomy helmet compatible hood which is always useful for climbing. When you're not climbing, the volume adjustment on the hood gives you a decent close fit on a helmet-free head.



The Proton LT in size medium weighs 385g on my scales, which makes it pretty light for a synthetic jacket - in fact it's lighter than some of the entries in our Lightweight Down Jackets group test. Not only is this great when you're wearing the Proton LT as there's no weight to restrict your movement, but it also means that you can quite happily throw it in your bag as an extra warm layer without having to worry about it weighing you down.

The Proton LT feels really light and looks stylish  © UKC Gear
The Proton LT feels really light and looks stylish
© UKC Gear

Warmth and Windproofing


The insulation in the body is a 100% polyester called Coreloft Compact 80 (presumably 80g/m2 though Arc'teryx don't provide this info up front), while in the hood it's Coreloft Compact 60. This has a decent loft, and seems warm for its fairly minimal weight.

For rock climbing in the winter the Proton LT is a great choice for an outer layer: when it's cold you can put it on over your fleece for some extra protection whilst you're warming up. In fact, the jacket is so light that you don't have to remove it once you get going - you hardly notice that you're wearing it. Being an extremely breathable jacket you could never expect the Proton LT to be very windproof, however it does keep some of the wind off and it can also handle a light shower.

Wearing the Proton LT Hoody on the outside on a winter mountain day, you do feel the wind  © Toby Archer
Wearing the Proton LT Hoody on the outside on a winter mountain day, you do feel the wind
© Toby Archer


It's easy to be sceptical of Arcteryx's description of the Proton LT: "a breathable insulation package to manage the dynamic needs of mountain pursuits and perform as a self-regulating mid layer for a variety of high output activities" but, actually, that's sort of what it does. There has been a trend for "active insulation" in recent winters: synthetically insulated jackets made with air permeable outer layers that allow wind through. This takes away excess heat and sweat but then again if the air permeability means wind takes the warmth away, it's not really successful insulation, is it? This was on my mind early in the morning back in the dog days of December, walking up from Glenridding - soggy snow on the ground, the temperature just above freezing, and winds barrelling down the valley. With just a base layer under the Proton the lack of windproofing was apparent, nevertheless the Proton gave more wind resistance than my normal mid-layer of grid-hooded microfleece. Between the strongest gusts, the Proton works like a more normal light insulated jacket and feels cosy but the air permeability seemed to work well to stop me over-heating and sweating move than normal. The hood is easily pulled up and down as you need more or less warmth.

I kept wearing the Proton as my outer-layer until cresting the ridge at the start of Swirral Edge where I pulled on a Gore-Tex over the top. Once under the hardshell the Proton LT is obviously completely wind-proofed and works as a warm insulation piece. It still seems much more breathable than other synthetic mid-layers I've tried, so even though climbing solo and not hanging around, I didn't feel I was overheating in it under the shell once up high on Helvellyn.

Subsequently I've used the Proton LT on pitched Scottish winter climbs; walking in wearing it as my outer layer and then climbing with it under my hardshell and have been impressed, including not needing to get my belay jacket out whilst leading two friends up a gully in Coire an t-Sneachda on a cold and blustery day.



The Proton LT uses Fortius™ Air 20 face fabric which Arc'teryx say is extremely durable - I have certainly not had any tears or holes from gritstone bouldering this winter (otherwise known as rubbing yourself against sandpaper) so that's a good sign, although I am always careful. Inside the jacket has something rather ridiculously called a Dope Permeair™ 20 liner, which feels lovely and soft. Overall the jacket looks and feels top quality and the materials are stretchy and light enough to enable the freedom of movement that the Proton LT is designed for.


I have only used the Proton LT in winter so far, but because of the air permeable nature of the fabric I suspect it wouldn't work so well as a super-light belay jacket for rock climbing in the mountains in the summer. For that sort of use, a more classic light synthetic filled jacket that is more windproof would work better. I'd say the Proton LT performs best as "active insulation" in colder weather - breathable and not too hot when you are working hard, and then as a cosy mid-layer once you pull a shell on.

Surprisingly, considering I've been wearing the jacket over just my base layer, it also seems quite whiff resistant! Being synthetic it is easy enough to chuck in the washing machine but so far this has been unnecessary despite plenty of long days in the mountains wearing it car to car.

Theo's loving his jacket  © Mike Hutton
Theo's loving his jacket
© Mike Hutton


Overall the Proton LT Hoody is an extremely lightweight, breathable and versatile jacket which is great as an outer layer for hillwalking, rock climbing or bouldering when it's cold, but also functions very well as a mid layer insulating piece for winter climbing. It also looks very stylish and will be a great general use jacket for when it's a bit warmer.

Arc'teryx say:

The Proton LT Hoody is equipped with a breathable insulation package to manage the dynamic needs of mountain pursuits and perform as a self-regulating mid layer for a variety of high output activities. Breathable insulation means excess heat and moisture can pass through the combination of air permeable fabrics and insulation. In addition to being extremely air permeable, the Fortius™ Air 20 face fabric has unrivaled hardwearing durability, over 60 times more durable in abrasion tests than the industry standard. Coreloft™ Compact 80 synthetic insulation in the body maintains excellent stretch recovery. The No Slip Zip™ keeps the main zipper from self-opening and the helmet compatible insulated hood gives additional warmth. Put it on, leave it on and stay focused on the activity.

  • Weight: 385g size M (our weight)
  • Sizes: XS-XXL (men) XS-XL (women)
  • Insulation: Air permeable Coreloft™ Compact 80 in body; Coreloft™ Compact 60 in hood
  • Fortius™ Air 20 face fabric balances air permeability and weather resistance with lightweight durability
  • Trim fit for athletic performance
  • Adjustable hood drawcords
  • Helmet compatible hood
  • Chest pocket with zip
  • Two insulated hand pockets with zippers
  • Articulated elbows and gusseted underarms
  • No Slip Zip™ front zipper
  • Dual back flaps on main zipper prevent wind penetration
  • Drop back hem and dual lower hem adjusters
  • DWR (Durable Water Repellent) finish

Proton LT hoody prod shot

For more info see

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17 Feb, 2020

Nice! Could we have your views on either the ME transition or the ME kinesis jackets? I'm in the market for a midlayer that is more windresistant than my standard fleece and would love to have your thoughts on these pieces.

17 Feb, 2020

i can't speak for the transition, but have worn the Kinesis and the Proton LT and tried the transition on in store.

The Kinesis is defininetly the most windresistant, maybe even windproof. The outer is thin like parchment. It dries really fast even in humid conditions but it's also fragile i guess. Dave MacLeod wears it in most of his videos while climbing so its either tougher then expected or being sponsored gets him a new one everytime it got shredded.

The inner fuzzy liner is some hollow core yarn insulation, like the one used in the Proton FL or the Rab Paradox Light. But in this case its fuzzy like polartec alpha direct and not lined. The marketing claims that its an evolution of Polartec Alpha with better microclimate and thermal management and wicks faster. After some use i can agree. Looking at the new gear from the ISPO this hollow yarn might be the next step for action suits. I think it mimics the properties from polar bear fur? It has a really cozy feeling and wicks sweat really fast in combination with the outer. I wore it with a LS Tee hiking in 15°C and for running aerobically, layered with a ME solar eclipse hoody around 0°C. I had both times a super comfortable feeling, minimal sweat build up while feeling warm and no wind came through.

I do have a Salewa Pedroc Pertex-Quantum+Polartec Alpha 60g/m^2 jacket that gets clammy faster and isnt as warm as the Kinesis. So it made the salewa pretty much obsolete. Only thing that bugs me is that the fuzzy insulation grabs onto your layers beneath. The Hood is roomy enough for a helmet and it packs into a pocket twice the size of a packed Squall or a 2l bladder/1,5l Nalgene. Mine does also have a dual slider zipper which is nice. Not sure how good it insulates while being static but i might use it in summer for climbing/belaying.

Summary: Current go to Jacket for aerobic activities for changeable weather with no to minimal sunshine.

Regarding the new Proton LT i can't say much. Haven't used this one that much and mostly walking to the gym. But you probably read the nice review above anyway. But i can compare fit and wind resistance on the Transition in comparison to the LT. Both seem to be comparable in terms of warmth and warmer then the Kinesis. I wear a medium in both brands for jackets.

The Proton LT fits me better and is less restrictive around the shoulders. The Transition feels a bit slimmer in waist and shoulders. The medium already felt tight around the shoulders. The Proton has more room to layer and offers more freedom of movement, but is still tailored well. The Transition is also slimmer as the Kinesis.

The Proton is marginally less wind resistant and the Coreloft insulation doesn't need stitching which is also good against cold spots.

Summary: Try it in the shop. It comes down to how they fit. Both jackets are warm for activities in the negative degrees and breath well, but i feel personally that the design and fabrics on the Proton are better.

17 Feb, 2020

How does the Atom LT compare with the Proton LT?

18 Feb, 2020

Nice to see Arcteryx recognising the qualities of continuous filament

We've a Kinesis review coming out on Friday

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