The Atom LT from Arc’teryx is a legend. This popular synthetic piece crosses over between daily wear and backcountry use as well as anything on the market, thanks to its truly impressive balance of warmth, comfort, and styling.

Arc’teryx Atom LT Hoody
Arc’teryx Atom LT Hoody

Arc’teryx gave the jacket a thoughtful revamp a few seasons back, and we put it to the test in a range of shoulder-season and winter-like conditions. The verdict: the latest model is as versatile as ever, but tweaks to the fit (it’s a little longer) and improved durability should only widen its appeal. Below we break down the Atom LT’s performance. To see how it stacks up to the competition, see our articles on the best synthetic jackets and best midlayers.


The Arc’teryx Atom LT Hoody has synthetic insulation, so it won’t rival down fill in terms of warmth or packability. Having said that, 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. This low-profile design puts it on par with other leading synthetics like Patagonia’s Nano Puff and The North Face’s ThermoBall. In addition, its weather-resistant shell does a nice job cutting wind, and the tall collar, adjustable hem, and fantastic hood (more on this below) help when you need to hunker down in cold temps.

From our experiences with the new Atom as well as prior generations of the jacket, we are comfortable wearing the hoody model 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 recent hike with temperatures hovering in the high 20s Fahrenheit. But for static use, such as sitting around camp when the sun goes down, we’re switching to a down jacket or adding a shell overtop. For a similar design with more warmth, Arc’teryx also makes the Atom AR 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).

Weather Protection

Featuring a weather-resistant shell, synthetic insulation, and excellent coverage from its collar and adjustable hood, the Arc’teryx Atom LT does a nice job in light to moderate precipitation and wind. The Tyono face fabric feels slightly more substantial than other leading synthetics we’ve worn—including the Patagonia’s popular Nano-Air—and it’s finished with a DWR treatment that effectively beads up water and snow. Fleece isn’t a great wind blocker, so the side panels will let in strong gusts, but its hard face exterior repels moisture effectively. To be clear, the jacket will start to soak up water in extended rainfall, so it shouldn’t take the place of a waterproof rain jacket or hardshell. But if you do happen to get caught in a surprise storm, the jacket can hold its own for a short period of time. And if water happens to get into the insulation, the good news is that the Coreloft fill will continue to provide warmth (something duck and goose down will not do).


One of the compromises of the Atom’s efficient warmth and decent weather resistance is breathability. Unlike active-insulation jackets like the Patagonia Nano-Air, Black Diamond First Light, and even Arc’teryx’s own Proton LT, 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. That being said, we’ve found the jacket excels for moderately strenuous activities like hiking and downhill skiing (it’s a near-perfect midlayer in this case), and its warmth is a benefit if the temperatures are particularly cold (we’ve used it for cross-country skiing in the Midwest). In the end, those looking for a high-performance piece will be better off with the Proton LT, but the Atom is the more versatile design if you plan to wear it casually and around town.


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