The original Nuclei was pretty much perfect — in my review (link) when this jacket was first released back in 2014, my only complaint was that it “didn’t stuff into its own pocket.” Since that time some of my preferences have changed, and after several less-than-ideal experiences with pocket-stuff-sacks, I’ve now come to prefer separate, stand-alone, stuff sacks. If I were to review the original Nuclei today, my main complaints would be a lack of interior drop pockets and the absence of a double-slider zipper on what is purported to be an all-around insulated alpine hoody.
The new version of this lightweight synthetic jacket came out in Spring 2020, the Nuclei FL, and the new moniker comes with several notable improvements. Most noticeable are the two interior drop pockets, though functionally more significant is the switch from Coreloft 80 g/m2 to Coreloft Continuous 65 g/m2 throughout. The double-slider zipper is still, unfortunately, conspicuously absent.
Thanks to several years of technological improvements, the newer Coreloft Continuous insulation is not only lighter but also warmer and more breathable. As the name implies, the key difference in the fills is the fibre construction: the original Coreloft is a clumped-fibre insulation designed to mimic down, while the newer Continuous version is more akin to a sheet that can be suspended between the inner and outer fabrics of a jacket. It’s also a bit lighter: 65 grams/metre vs 80 grams/metre for the older tech. The key gain with a sheet-woven style of insulation is increased breathability from the ability to use a looser fabric weave (because you’re not worried about keeping the fill from escaping) while at the same time less baffling increases the outer fabric’s weather resistance and warmth retention (due to the lack of stitching in the face fabric). Advances in synthetics have improved the actual structure of the fibers, resulting in a warmer jacket, even though it doesn’t quite mimic down in structure as closely anymore.
Thanks to this lighter and different style of fill, Arc’teryx were able to utilize a tougher outer shell fabric for increased durability and better weather resistance. The Arato 10r fabric continues Arc’teryx’s remarkable achievements in continually creating lighter and stronger fabrics that are somehow more abrasion resistant than before: after close to a year of use, my pre-production sample still looks as good as new (mine arrived around September 2019, almost a year ago).
In terms of performance, I’ll happily use the Nuclei FL as a belay jacket down to around -10C and it keeps me nice and warm (provided I layered properly to begin with!). On sunnier days I’ll take it down to -15C or so, though I do remember one particularly overcast and windy day where even at -5C or so I shivered more than I would’ve liked. This is, of course, winter use when I’m wearing multiple other layers: much like the original, this is a great all-around light-use jacket, and it excels on chilly spring/summer alpine days.
The hood remains much the same as before: somewhat helmet compatible but it feels much better over a bare head. Again, a nod to the summer-oriented design of this jacket.
Other than the somewhat invisible improvements to fabric and fill, the most noticeable addition are the two interior drop pockets. Big enough to fit a pair of gloves each, they’re conveniently located just inside the hem at the zipper line. I really appreciate having a place to stash gloves, toques, and other small essentials when on belay — a marked improvement on the original Nuclei, which didn’t have any inside pockets other than a tiny place to stow the stuff sack (useless save for maybe a stick of lip-chap).
Still absent, unfortunately, is that double-slider main zipper. Though the hem has enough stretch to zip over a harness with a pair of ice clippers, I would have preferred a double-slider with a hem snap for increased versatility. I somewhat understand the thought process, especially if viewed solely from a spring/summer design perspective: rock climbing, even multi-pitch or mid-summer alpine with a harness loaded down with dozens of cams and other pro, still requires a lot less physical space and room around the harness waistbelt than a couple of ice clippers loaded with ice screws (the things are damn bulky!). However, I would trade a bit of extra weight and additional cost for the overall improved functionality of a double-slider zipper.
Speaking of weight, it hasn’t changed at all: my Men’s Medium weighs exactly 300-grams, the same as my original Nuclei. Crucially, at the same weight, it offers more warmth, a slightly roomier fit, and those inside drop pockets,
The stuff sack adds another 8-grams to the equation, should you bring it along. Arc’teryx has been using this style of stuff sack for a while now: the stuff sack, inside-out, attaches to a loop inside one of the pockets, when used to actually stuff the jacket it reverts to outside-out, protecting the jacket while all the time remaining attached to the Nuclei to prevent loss. I will say that I do not like this when the stuff sack ends up inside the hand pockets, but I have no issues whatsoever when the attachment is inside one of the interior pockets (like on this jacket).
Another thing that Arc’teryx haven’t messed with is the fit: this is still a relatively trim-fitting piece through the body but with long sleeves, roomy shoulders and a helmet-compatible hood. The hem also feels a bit longer than on the original, with a more pronounced drop in the back for better ass coverage. Do keep in mind that it is designed as a summer-weight piece, which means it isn’t quite as roomy as winter-sized layers: for spring/summer use, stick with your usual size, but for dedicated winter use I would recommend going one size larger.
A rather marked change, however, is the higher cost, though this seems to be more a function of economics as seemingly everything has gone up in price in the past few years: the Nuclei FL retails for $350 as compared to the original’s $260 (Canadian retail prices). This is on the higher end of the lightweight synthetic hoody spectrum, which seems to range from around $250-375 (again, Canadian dollar), though it is in line with Arc’teryx’s typical premium positioning and superb quality, backed by a solid warranty (which, yes, I’ve used a number of times on personally-purchased items and have always been impressed with the quality of repairs and customer service).
Overall, this is my new favourite lightweight synthetic: I’ve been using it as either a mid-layer or approach piece on colder days, and a belay jacket on the warmer ones. It layers exceptionally well, and packs down small enough that I bring it along almost everywhere.
Notable competitors I’ve used/tried/am testing out:
Rab Xenon X (SS16): I had one for a while, and it had a double-slider zipper which I love, but for some reason I didn’t like it all that much. Honestly I can’t even remember when or why I got rid of it: clearly not a memorable piece for me.
Patagonia Micro Puff (FW17): This came out between the original Nuclei and this new FL variant and I so wanted to love it because it solved my main issue with the ‘original’ Nuclei: no interior drop pockets. However, the hood isn’t helmet compatible, and it still lacks a double-slider zipper. Still, I love the fit and warmth of it, and I have one as an around-camp layer.
Patagonia DAS Light (FW20): Brand new on the scene, and in my closet, this uses the same insulation as the Micro Puff but has a helmet compatible hood and a double-slider zipper. But, it loses the two interior drop pocket — WTF Patagonia?! Still, it has promise (maybe I need to get a sewing machine…)
Arc’teryx Alpha IS (FW17): Quite possibly the best light-to-mid-weight synthetically insulated jacket you can buy. And it’s waterproof. Also 3x more than the Nuclei FL… but does awesomeness have a price?? (Review here.)
Final word: I’ve been trying to downsize the frankly absurd number of jackets I have ended up with into one from each category (there are eighteen categories, by my latest count, in case you’re curious). The Nuclei FL has taken the spot as my lightweight synthetic hoody of choice, and now that I’ve had a chance to use it on a few summer scrambles, I love it even more. It’s an absolutely perfect spring/summer insulation layer, and extends into colder weather use as well. Highly recommended.