Arc'teryx Atom vs. Proton vs. Nuclei: Differences and Reviews 2025

Moisture-resistant outer face fabric
Breathable
Lightweight
Compressible and packable
Insulated
Wind resistant
Versatile

Wind resistant
Abrasion resistant
Air permeable
Water resistant

Windproof
Great warmth-to-weight ratio
Compressible and packable
Durable
Water resistant

3. Warmth

Resilient Coreloft Compact 60 insulation is breathable, warm, and light, performs if wet, and delivers loft retention that resists packing out.

The Arc’teryx Atom LT Hoody—along with its successor, the Atom Hoody—has synthetic insulation, so it won’t rival down fill in terms of warmth or packability. But this jacket makes a really nice fall and spring outer layer and also works great as a midlayer for snowsports and in frigid temperatures. It’s filled with 60-gram (g) Coreloft Compact insulation everywhere but the side panels, which are a stretchy midweight fleece. In addition, its weather-resistant shell does a nice job cutting wind, and the tall collar, adjustable hem, and fantastic hood help when you need to hunker down in cold temps.

In terms of warmth, the Atom LT was comfortable down to about 40 degrees Fahrenheit without much in the way of layering underneath. It certainly can go lower with a warm baselayer or if you’re on the move—it was an ideal outer layer on a hike with temperatures hovering in the high 20s Fahrenheit. But for static use, such as sitting around camp when the sun goes down, you need switch to a down jacket or adding a shell overtop. For a similar design with more warmth, Arc’teryx also makes the Atom Heavyweight Hoody, which ditches the stretch side panels and includes more substantial 120g Coreloft around the body and slightly less in the underarms (80g) and hood (60g).

Source:arcteryx.com

Air permeable Coreloft Compact 80 insulation regulates a comfortable micro climate. Coreloft Compact 60 insulated helmet compatible hood gives additional warmth.

With 80-gram Coreloft Compact in the body and 60-gram in the hood, the Arc’teryx Proton LT is a great match for high-output use in sub-freezing conditions. It has become most people go-to midlayer for backcountry skiing and cool-weather adventures, as well as while assembling gear on frigid mornings and throwing on post-ride as soon as I shed my sweaty bike jersey. If you are running in the conditions above freezing, the Proton can be too much jacket. If you are more sedentary like sitting around camp, the hoody is perfect in temperatures up to around 60 degrees Fahrenheit. The new Dope Permeair liner and 80-gram Coreloft in the body have significantly reduced the chill factor in cold and blustery weather, making ski transitions and sitting around camp considerably more enjoyable. And the dual back flaps on the main zipper are great, which reduce the risk of wind penetrating through the teeth (bonus: they also keep your facial hair from snagging).

Source:arcteryx.com

The jacket uses 65-gram Coreloft Continuous, which lofts almost immediately when the jacket is uncompressed—it self-inflates almost like a sleeping pad.

The biggest selling point of the Arc’teryx Nuclei FL is its warmth: this jacket is built for the alpine and has the ability to keep you cozy in harsh conditions typical of that environment. For insulation, the jacket uses 65-gram Coreloft Continuous. You will feel comfortable during inactive times in temperatures down to around 40 Fahrenheit. And the Nuclei FL’s low weight , this is quite remarkable.

Source:arcteryx.com

4. Breathability

One of the compromises of the Atom’s efficient warmth and decent weather resistance is breathability. The Atom runs fairly warm during high-output sports like ski touring. Its face fabric and lining do a good job trapping heat, and while the fleece side panels do help with releasing some hot air, overall ventilation is solidly middle-of-the-road.

Those looking for a high-performance piece will be better off with the Proton, but the Atom is the more versatile design if you plan to wear it casually and around town. The Proton LT truly excels in its ability to regulate body heat and keep me cool on long ascents. In a typical “breathable” synthetic jacket, heat only releases from the inside, but the Proton’s shell and lining allow air to flow from both the inside and out. This air permeability has proven to be a perfect match for backcountry skiing.

As for Arc'teryx Nuclei, this jacket is not meant to be worn during exertion. It’s great for hanging out at camp, transitioning in the backcountry, or standing at the belay, but it will overheat quickly once you get moving. If you’re on the hunt for a synthetic jacket to wear during activity, we’d instead recommend Arc’teryx’s more breathable Proton series (the Proton LT is the closest in warmth).

5. Weight and Packability

	Arc'teryx Atom	Arc'teryx Proton	Arc'teryx Nuclei
Weight	370g / 13.1 oz	400g / 14.1 oz	325g / 11.5 oz

The Atom doesn’t come with a stuff sack, nor is it designed to fit into one of its own pockets.
As the same, the Proton doesn’t come with a stuff sack, nor is it designed to fit into one of its own pockets. But it still only requires minimal real estate in your pack. If you’re a stickler for space, throwing the Proton into a small compression sack could likely get it down to the size of a water bottle.
Along with its warmth, the Nuclei FL’s weight and compressibility are two of its standout features. In its stuff sack, the jacket packs down to roughly the size of a 32-ounce Nalgene bottle, and it can easily be stuffed down further to the size of a large grapefruit. In a dedicated compression sack, the Nuclei FL can be reduced to the size of an orange.

6. Comfort

Comfort is the area where the Arc'teryx Atom excels most. You can wear it hiking or climbing and then to the grocery store or bar afterward, all without missing a beat. The interior lining is soft and smooth to the touch, the stretchy sides and relatively athletic cut give it fantastic mobility, and the Coreloft insulation creates a pillow-like barrier from the outside world. Tack on thoughtful touches like a fleece-like lining inside the hand pockets (for the back of your hands) and smooth cuffs, and the Atom is one of the coziest and most versatile jackets.

With 16 percent elastane along with articulated elbows and gusseted underarms, the Proton offers excellent stretch. Additionally, the lining and shell fabrics have a premium feel and excellent softness. Even when you have overheated in the hoody, the lining doesn’t grow sticky or clammy, and it slides nicely over baselayers without any bunching. And the sleeves have stretch-knit cuffs that make it easy to put on and take off the jacket while also reducing the risk of cold air or moisture entering at the wrists.

The Nuclei FL has a trim, athletic cut. Arc’teryx did a fantastic job with the Nuclei FL’s features. The hood (adjustable with one cinch at the rear) is far more comfortable with or without a helmet, the handwarmer pockets are set above a pack’s hipbelt instead of low by the waist, the waist drawcord stows inside the jacket so you don’t accidentally clip it when climbing with a harness. Though these are minor features, they add up to a significantly more comfortable jacket. Additionally, Nuclei FL is extremely comfortable both in fit and feel. Adn the liner is silky-smooth and remains that way even against sweaty, bare skin.

7. Fit and Sizing

The Atom with a little more length at the front and back (note: The latest Atom Hoody shares a similar fit but with additional room in the midsection for added mobility). It’s still a great length for wearing as a midlayer, but the extended dimensions will help for taller folks who have had sizing issues in the past. The cut of the jacket remains on the trim end, which is great for those who like an athletic fit.

Source:arcteryx.com

Proton LT has a trim cut but runs true to size.The Proton also is nicely tailored with no excess fabrics to bunch up under a hardshell jacket. If you’re looking to add multiple layers underneath, however, I’d recommend sizing up. All in all, it’s the kind of fit where you put it on and forget about it.

Source:arcteryx.com