80g of Coreloft insulation is used in the body and then there’s 60g in the side panels and sleeves, making for an overall warmth that packs a punch.
At just 325g overall the Arc’teryx Nuclei FL is by no means a heavy jacket either. One of the main contributing factors here is the outer shell, which is made from a fully windproof 10D nylon with a ripstop weave. It feels very, very thin. Not so thin that you’d need to worry about the fabric on the shoulders when wearing a heavy-loaded pack, but you’d want to be careful picking through any thick brush in it.
The hood, which has a semi-elasticated rim, is fully insulated so you won’t have any cold spots. It’s also designed to fit comfortably both over or under a helmet. It holds nicely thanks to the drawcord toggle at the back (a useful feature that you don’t always see on insulated jackets). There are also two toggles to cinch in the hem. The cuffs, as you’d expect, just have simple elasticated rims that hold nicely but they’re still loose enough to allow you to pull mountaineering gloves through them.
As for pockets, you have two zipped handwarmers and then two handy but non-closable ones for stashing gloves (or an OS map) on the inside.
Will Renwick, editor of Outdoors Magic
“Full disclosure. Due to the UK lockdown restrictions and the warm spring we’ve had, I haven’t been able to test this out in the conditions it’s made for so consider this more an ‘initial impression’ than a review.
“It’s certainly impressive right out of the box though, and from wearing it out on a couple of colder summer backpacking trips, it’s given off the scent of a very reliable mountain jacket.
“With its quality materials and tidy construction, it certainly appears well-made, matching the high standard of workmanship that we’ve come to expect from Arc’teryx.
“It’s a great jacket. One I can see myself calling upon right through winter.”
“The insulation is very impressive. As soon as the jacket is pulled out of the stuff sack, it starts to kind-of inflate, making the jacket feel extremely lofty and puffy like a down jacket.
“It feels very similar to the Patagonia Macro Puff, a jacket that provides an amazing amount of warmth and at a low overall weight. That jacket weighs a fair bit more than this though and it costs more as well. One of the bigger downsides of the Macro is that it has a ridiculous amount of stitching (that over time will get loose). This, on the other hand, features large panels/baffles and therefore minimal thread. I suspect that might mean it has a much longer lifespan than Patagonia’s similar offering.
“Another jacket this is similar to is the Rab Xenon X which I took with me on a 300-mile backpacking trip on the Cambrian Way a few years ago. I loved that jacket for its impressive warmth-to-weight and the general loftiness of its fill. This, the Nuclei FL, seems to trump it in those stakes by a fair whack though I reckon.
“As for the fit, I’m usually a men’s Medium and found the Size M fitted me perfectly. It hits that sweet spot where it feels loose and comfortable but doesn’t appear baggy. Thanks to that compressibility of the insulation, I’d say most waterproof jackets will fit over it – all but tight lightweight waterproof jackets for trail running perhaps.
“Just a few couple of very minor niggles I had though. First of all, the drawcords on the hem are a little fiddly and any excess bungee has the potential to snag on your gear. I also think a chest pocket would’ve made up for the fact that the handwarmer pockets can’t really be accessed when you’re wearing a harness or a backpack with a hipbelt.
“Anyway, it’s a great jacket. One I can see myself calling upon right through winter. Based on my initial impressions, if I had to choose between this and its nearest two competitors, I think I’d pick this.”
Brylee Geddis, Apparel Designer, Arc’teryx
“The Nuclei Fl was originally launched as a lightweight climbing belay jacket back in 2015 but removed from the line just two years later. Climbers loved it and missed it. After it was pulled from the line, Arc’teryx athletes and users continued to ask for the Nuclei to return. Advancements in materials development allowed our team the opportunity to make some updates including warmer insulation, and better loft retention than the previous Nuclei. The women’s and men’s versions were designed separately to fit adjustments to our different body types and we added a helmet compatible hood and two dump pockets for storage.
“It is vital to us when updating a product that the next generation surpasses its predecessor.”
“When tasked with resurrecting a “cult classic” the expectations are very high. I’m proud to have collaborated with fellow designer and accomplished climber JJ Mah on this. It was the perfect opportunity to bounce ideas off one another to come up with the best product possible.
“It is vital to us when updating a product that the next generation surpasses its predecessor. We spent countless hours testing fabrics, insulation, and other materials. We’re always trying to find the right balance of weight and durability. Interestingly enough we spent a lot of time on the stuff sack – testing out materials and construction strengths as the athletes reported the importance of having a strong attachment point (you don’t want to lose your jacket mid climb!).”