Arc'teryx Atom vs Proton: which insulated jacket should you buy?

The Atom and the Proton are both Arc'teryx synthetic insulated jackets, they both come in hoody versions, and preloved they sell for similar money. So which one do you actually want? I handle a lot of both, and the difference comes down to what you'll be doing in it.

The quick answer

• Atom: the everyday one. Blocks wind well, stretchy fleece panels down the sides, and the hood is the better one. Best for town, travel, dog walks and wearing under a shell.
• Proton: the active one. Tougher, more air-permeable face fabric and a bit more warmth in the body. Best for climbing, ski touring and anything where you're working hard and getting sweaty.

Arc'teryx Atom

The Atom LT (now just called the Atom) is Arc'teryx's best-selling jacket. It uses 60g Coreloft synthetic insulation in a light nylon shell (Arc'teryx call the fabric Tyono), with stretchy fleece panels running from the armpit to the hem. Those side panels are what make it so comfortable and breathable when you're walking about.

The shell is very good at keeping wind out, and the Atom hoody gets Arc'teryx's StormHood, which fits close and moves with your head. It also packs down well and sits neatly under a Gore-Tex shell, which is why so many people treat it as their everyday jacket.

There's also a lighter Atom SL with less insulation, and the warmer Atom AR, now called the Atom Heavyweight, which drops the big fleece side panels for more warmth.

Arc'teryx Proton

The Proton LT (now the Proton Hoody) is built for moving fast in the cold. It has more insulation in the body (80g Coreloft, with 60g in the hood) and a tougher, air-permeable shell fabric called Fortius Air. That fabric lets heat and sweat escape while you're climbing or skinning uphill, and it stands up better to rock, rucksack straps and ski edges.

Reviewers find the Atom better at blocking wind when you're standing still, and the Proton more breathable when you're working hard. The Proton hood is a standard insulated hood rather than the Atom's StormHood. There are lighter versions too (the Proton FL, later Proton SL), plus the Proton Hybrid with Gore-Tex Infinium panels for extra weather protection.

Side by side

• Warmth: Proton is a touch warmer in the body. Atom LT and Proton LT are close enough that most people won't notice day to day.
• Wind: Atom wins when you're standing about.
• Breathability: Proton wins when you're working hard.
• Durability: Proton's face fabric is the tougher of the two.
• Hood: Atom's StormHood is the better everyday hood.
• Style: the Atom is the classic look. The Proton is a bit more technical, with a slightly cleaner front without the fleece sides showing.

The new names

In 2024 Arc'teryx renamed most of the range, which confuses a lot of people buying preloved. Roughly:

• Atom LT is now the Atom
• Atom AR is now the Atom Heavyweight
• Atom SL is becoming the Atom Lightweight
• Proton LT is now the Proton Hoody
• Proton FL became the Proton Lightweight, then the Proton SL

The designs and fabrics barely changed, so an older Atom LT is basically the same jacket as a new Atom. If you want to check exactly what you've got, the model number on the care label can be looked up on Arc'teryx's ReBird trade-in search.

Which should you buy?

If you want one warm jacket for everyday wear and the odd walk, get the Atom. If you climb, ski tour or run hot and want something that copes with hard use, get the Proton. Preloved, both regularly go for well under half their RRP.

For sizing, see our Arc'teryx sizing guide. For the full Atom story, read Arc'teryx Atom jackets: history and which one to buy.

In stock now

• Proton LT Hoody 2019, Slate Blue, Men's Small
• Proton Hybrid Hoody 2022, Multiverse, Men's Medium
• Atom LT Hoody, Grey Blue, Men's Medium
• Atom LT Hoody 2021, Vitality Blue, Men's XL
• Atom LT Vest, Grey Red, Men's XXL

Every piece is checked by hand and cleaned before it goes out. See all Atom jackets or all Arc'teryx in stock.