Robust highly breathable insulation which copes with a wide range of activity levels if temperatures are cold enough.
A number of manufacturers are now producing highly breathable synthetic insulation pieces and I was keen to try this new approach to staying warm in winter. So first up this is a layering piece and not a belay jacket – you will be disappointed if you purchase the Proton LT with a view to using it as a conventional belay jacket.
The Proton Light Hoody is the lighter of the two offerings from Arc’teryx coming in at around 400g. Described as a “highly air permeable synthetically insulated alpine jacket” the Proton LT Hoody uses Arc’teryx’s own Coreloft™ Continuous 65 for insulation with a Fortius™ Air 40 shell that provides some water resistance and a degree of wind protection. The Coreloft™ Continuous does not seem to be as compressible as the standard Coreloft™ found in my Nuclei FL but it has been developed to be more breathable. Simple elasticated cuffs, an adjustable helmet compatible hood, two hand warmer pockets and a stretchy chest pocket round out the feature set. The cuffs have a cleaver dart of stretchy material allowing for a slim fit whilst still easily slipping over a typical leading glove but they are best suited to going under bulkier glove cuffs. The basic hood will fit over a helmet but lacks a peak having a simple volume adjuster on the back and is elasticated around the face. At the risk of sounding like a broken record the hand warmer pockets could do with being a smidgeon higher as they foul the harness waist belt but are still accessible. The stretchy chest pocket will accept a phone, sunnies or a snack bar but is pretty slimline. Trying the Proton on in my living room it was clearly heavier and bulkier than my Nuclei FL but with a more textured tough shell. The fit was excellent with plenty of mobility in the arms and no problems with the hem line pulling out of a harness.
The Proton LT Hoody’s first outing was a rather mundane steady bike ride to yoga and then onto the Depot (bouldering wall) with temperatures around 2-3°C. Having expected to overheat a bit I was surprised to find this was not the case and the jackets air permeability was really apparent coasting downhill. It’s difficult to describe, the Proton is clearly not windproof like the Nuclei or similar jackets and there is a noticeable exchange of air but the wind doesn’t ‘cut’ into you, the combination of Coreloft and Fortius provide a degree of baffling which works well when you’re active. The Proton LT Hoody seemed to offer equal breathability compared to a heavyweight fleece but increased warmth and improved wind resistance (compared to non-windproof fleeces). A late autumnal trip to the Lakes and a frosty morning start found me wearing the Proton LT wandering up to Dale Head from Borrowdale. Again I was surprised how long I could keep the Proton LT on before having to stash it in the pack as I heated up, the high degree of breathability certainly helped regulate temperatures but in the end it is an insulated piece and working hard uphill I usually end up wearing little more than a base layer. With the Scottish winter season proving increasingly disappointing a trip to Cogne allowed for a better test of the Proton LT’s cold weather performance. In the interests of honesty I must confess that to begin with I thought the Proton LT Hoody was going to be far too warm for the approach. However the Proton LT coped with the fairly flat valley walk ins followed by relatively short steep final approaches to the ice falls surprisingly well, its breathability and the ability to fully unzip to dump heat allowed me to walk to the base of Patri without needing to stash it in the sac or feel uncomfortable wearing just a base layer underneath. Temperatures were probably around -5°C on the approach and dead still.
Arriving at the base of the route simply zipping up the Proton LT left me comfortably warm whilst racking up and beginning the circus that is climbing a popular mega classic in Valnontey. Arriving at the base of Candelone Di Patri in the shade we spent a good 30 minutes in typical Brit fashion queuing only to see four teams embarking up the route and another about to set up, crossed ropes, over-faced leaders clipping into axes. Joy! Throughout the time I was stood around I never felt cold and had no need of a belay jacket. We abandoned plan A and climbed Di Patri, wandering across and the abbing down Candelone Di Patri once things had quieted down. I remained comfortably warm on the belays and didn’t overheat whilst climbing in the Proton LT.
The range of activity that it can cope with is impressive but there is a proviso; the temperatures obviously have to be reasonably cold but if that’s the case you can go from pretty much static to full on climbing mode without having to shed or don layers. With just a base layer I found the Proton LT ideal for active use once temperatures headed toward 0°C, which is pretty ideal for ice climbing and winter mountaineering. The Proton LT doesn’t feel restrictive or bulky and its tailored cut allows you to climb without impediment making it a great ice climbing jacket. The robust outer is also re-assuring with all those spikey screws and picks about 😉 As things get colder you could add another layer beneath but the coldest it got during the review period was -6°C and I never used anything but a base layer. The shell also sheds the typical drips you get when ice climbing but would need a waterproof over it for more ‘Scottish’ conditions.
The Proton LT is a strong entry by Arc’teryx into the highly breathable synthetic insulation market. It definitely works very well once the temperature starts to drop toward 0°C and to be honest I think it will take a while before I discover all its possible uses. If you’re working hard uphill on a long alpine approach it will likely be too much even in winter but if you’re accessing climbs via uplift or more moderate walk ins it may be perfect – you can of course always stash it into a pack where it compresses better than the equivalent warmth fleece.
Richie is the enthusiastic amateur of the team. Enjoying all aspects of climbing especially alpine, winter and his local grit . Having managed to survive the vagaries of both fluorescent Koflachs and rainbow tights in the 80s he looks forward to a more stylish future. A shady past in mountain marathons and adventure races, including the Marathon des Sables, means he’s an advocate of fast and light. Though the former is debatable if you’ve seen him on a tricky lead!