Arc’teryx Atom Hoody vs Atom SL: 2025 Review & Comparison

Overview

The Arc’teryx Atom Hoody and Atom Jacket may well be Arc’teryx’s best-known product line, and for good reason. For more than 15 years the Atom has deftly blended performance, comfort and style, winning over customers with its durability and versatility. In 2023, the Atom LT underwent a name change, becoming simply the Atom Hoody and Atom Jacket in both men’s and women’s versions. The Atom SL is the "superlight" version available for men and women, and it was just updated for spring 2025. (Point of clarification: Arc'teryx briefly renamed the women's version the Atom Lightweight but has returned to the SL moniker for 2025.) 

Naming conventions aside, what hasn’t changed are the things that continue to make the Atom, in all its iterations, one of our favorite Arc’teryx products: high-performance synthetic insulation that works as either a midlayer or outer layer for both casual wear and higher-output activities. But with three versions - Atom Heavyweight (formerly called the Atom AR), Atom, and Atom SL - to choose from, it’s important to understand their differences as well as the ideal uses of each. 

In this review, we take a closer look at the Atom (LT) vs Atom SL. If you're debating between the Atom and the Atom Heavyweight, we compare them here.

Bottom line: The Atom Hoody is a versatile and comfortable midweight insulated jacket that provides a winning combination of warmth and breathability during colder weather. The Atom SL takes a noticeably more minimalist approach, making it a more breathable but significantly less warm option for high-output activities during chilly spring and summer outings.

• If you want a year-round performer capable of keeping you warm on its own or as a midlayer, go with the Atom. 
• If you need something just to help keep the chill off during high-output activities like trail runs and alpine summits in the spring, summer and fall, the Atom SL is a great choice.    

Before we go any further, here’s how Arc’teryx compares the Atom Hoody to the Atom SL Hoody.

And if you need help sorting through Arc'teryx's dizzying number of jackets, we think the Arc'teryx jacket finder is a worthwhile tool. 

If you are interested in the Atom SL, then you should also check out our in-depth look at the Patagonia Nano-Air Ultralight.

Recent updates to the Atom and Atom SL

Arc'teryx dropped revised versions of the Atom (hoody, jacket and vest) as well as the Atom SL in February 2025. The only real update to the Atom (LT) line is the across-the-board use of FC0 DWR, which is a PFAS-free durable water repellent finish. 

The Atom SL received more substantive updates in this latest refresh, including:

• Fortius Air 20 fabric replaces the Tyono 20 used in previous versions. Though both are made from recycled nylon, the Fortius Air is more breathable than the Tyono. 
• Coreloft Stretch insulation replaces the Coreloft Compact insulation previously used. Both are the same weight (40gsm). We're waiting to hear back from Arc'teryx about the switch. 
• Octa™ Fleece side fleece panels are lighter weight and more breathable than the fleece in previous versions of the Atom SL. 
• Although still not insulated, the Atom SL's StormHood is no longer stowable
• The new version is slightly heavier (9.9oz/280g in men's medium) than the old version (9.5oz/269g)

Atom vs Atom SL: Warmth

The Atom (LT) Hoody is clearly the warmer option when compared to the Atom SL Hoody, and it’s not really close. There are three factors that make the Atom warmer than its SL counterpart:

1. The Atom Hoody uses Coreloft Compact 60 insulation, versus the Coreloft Stretch 40 insulation of the Atom SL. 

   The Coreloft Stretch 40 g/m2 used in the Atom SL is Arc'teryx's lowest density (1.2 oz/yd2) Coreloft insulation. The only two Arc'teryx jackets insulated with 40 gsm Coreloft are the Atom SL and the Proton Hybrid (Men's - Women's - read review).
   
   This is one of the factors that makes the Atom SL exceptionally light, especially compared to the Atom (9.9oz/280g vs 12.5oz/355g). The Atom uses Coreloft Compact 60 g/m2 synthetic insulation, which offers quite a bit more warmth for the weight. Is the 75-gram difference between the models significant for you and your needs?

2. The Atom Hoody is insulated throughout, whereas the Atom SL is insulated only through the body

   That’s right, the Atom (LT) Hoody and Jacket are insulated everywhere - body, sleeves and hood. The Atom SL, on the other hand, is insulated only through the chest and back. Think of it as an insulated vest with windbreaker sleeves and hood. The sleeves of the Atom SL are mesh lined beneath their Fortius Air 20 nylon exterior. This difference obviously results in a significant warmth disparity between the two models. 

3. The Atom (LT) Hoody has a looser fit than the Atom SL

   As a result, the Atom (LT) Hoody trap more air between it and your body, which adds to the insulating effect. The Atom also offers two hem adjustment drawcords to the Atom SL’s one, making it a bit easier to cinch the jacket around your waist and prevent heat from escaping and cooler air and wind from entering. 

Our extensive temperature ratings of Arc’teryx jackets, including the Atom series, is below:

Atom vs Atom SL: Breathability & Ventilation

The Atom line is noted for its breathability, but it varies between models. The Atom (LT) Hoody is extremely breathable, but the Atom SL is even more so. We’ll explain.

The Atom uses the Tyono 20-denier nylon fabric, which is air permeable but not nearly to the extent of the Fortius Air 20-denier fabric now used in the Atom SL. It's worth noting that Arc’teryx’s Proton line also employs the Fortius Air fabric. We compare the Atom jackets to the Proton jackets here.

But face fabric is only one variable of breathability. Another significant factor is mechanical ventilation. This is where the Atom’s side fleece panels work spectacularly. 

The stretchy fleece panels placed along the sides of the Atom (LT) Hoody and Atom SL help prevent overheating by dumping excess heat. Think of them as pit zips on steroids. They're also great for mobility no matter your activity, stretching and moving with your body.

And while both the Atom (LT) and Atom SL feature these fleece panels, the size difference of the panels between the two models is significant and therefore makes a noticeable impact on breathability. The quality of the fleece is different as well, with the Atom (LT) using noticeably heavier weight fleece as compared to the lighter fleece panels of the Atom SL. 

Here's a look at the side fleece panels of the Atom SL. Note how the fleece runs all the way from the hem to the cuffs. 

Now here are the Atom LT’s side fleece panels, which extend only from the hem to the armpit but are also about an inch wider than the Atom SL’s panels. 

The first time I wore these jackets, I assumed the wider panels of the Atom would make up for the longer panels of the Atom SL and provide equal ventilation. But that’s not the case. In reality, the added breathability of the Atom SL from the extended fleece panels is readily apparent, which is a good or bad thing depending on how you plan to use your jacket. Personally, I’m a fan of the added breathability, especially when I’m using my Atom SL for high-output activities in the spring and fall.  

Atom vs Atom SL: Weather Resistance

Those big side fleece panels on the Atom come with a cost, however: reduced weather resistance. When the wind is blowing, both models invite the wind inside. A lot. This can be a good thing if your output is high or if you naturally run warm. But when you don't want the wind in, there's nothing you can do about it. 

This is why we consider the Atom SL more of a niche jacket than an all-around performer. When comparing its breathability to its wind resistance, the Atom SL leans way hard on the breathability end of the spectrum. 

The Atom (LT), on the other hand, is more balanced, even with its own fleece side panels skewing toward breathability. 

Both models of Atom will repel a moderate amount of moisture for a short period of time, but they are not waterproof. The Atom's Tyono 20 nylon face fabric and the Atom SL's Fortius Air 20 are both treated with a FC0 DWR finish. We’ve been impressed with their ability to shed precipitation, but they will eventually soak through. If you’re expecting sustained rain or snow, bring a waterproof shell as an outer layer.

Atom vs Atom SL: Fit

Arc'teryx says both the Atom and Atom SL are "fitted," but there's some slight variation between the models. The Atom Hoody and Atom Jacket are a bit roomier than the Atom SL. So we would describe the Atom SL as fitted, while the Atom (LT) is somewhere between fitted and regular. 

The fit differences underscore the differing uses of each model. The Atom (LT) can be used year-round as both an outer layer or midlayer, with the fit being sufficient to go on top of a baselayer as well as underneath an outer layer like a shell. The Atom SL is a spring/summer/fall piece for higher-output activities or when you just barely need some additional warmth (think insulated windbreaker).

As for length, expect near identical specs between the two. For example, the Atom and Atom SL share a rear center-back length of 29 inches in men's size medium. 

Atom vs Atom SL: Pockets

Both models have two handwarmer pockets with hidden zippers. The pockets on the Atom (LT) are fleece lined on one side and nylon on the other, while both sides of the pocket are nylon only on the Atom SL. 

Only the Atom (LT) has an internal zippered chest pocket, which is appropriately sized for stashing your phone, credit cards, key or other smaller items. The Atom SL has no interior pockets, befitting its position as a fitted lightweight jacket for high-output activities. 

Atom vs Atom SL: Hood

The Atom (LT) Hoody has an insulated and adjustable StormHood that is large enough to maybe fit over some climbing helmets but certainly not over a ski helmet. The hood is not removable or stowable.

The StormHood on the Atom SL is non-insulated nylon. It is adjustable with a single pull cord at the back of the hood, and it has a close-to-the-head fit that will easily fit over any type of helmet. We appreciate the shaped visor that provides structure to the front of the hood above your eyes. But the hood on the latest iteration of the Atom SL is not stowable. Previous versions allowed you to roll the hood inward and use an attached button to form it into the jacket's collar.

Atom vs Atom SL: Cuffs

Both the Atom (LT) and Atom SL have stretch cuffs, but they’re executed differently. The cuff on the Atom (LT) encircles the entire wrist (see photos), while the cuff on the Atom SL incorporates the edge of the fleece side panel on the inside of the wrist and the hemmed Fortius Air face fabric on the outside of the wrist. We think both cuff styles are functional and comfortable.

Summary

We really like wearing both of these Atom models, but they are not interchangeable. In fact, now that the Atom SL is made with the highly breathable Fortius Air 20 fabric, they feel similar in name only. 

The Atom Hoody (or hoodless jacket, depending on your preference) is a comfortable insulated jacket that breathes well for moderate activities and can be used year-round for warmth. It's a solid all-around performer that goes head to head with the Arc'teryx Proton Hoody (check out our comparison here) as one of our favorite go-to midweight jackets.

The Atom SL Hoody, on the other hand, is a highly breathable, lightly insulated jacket that will provide just enough warmth and weather protection when it's too chilly for a single layer. Consider the Atom SL if you're a runner, hiker or climber looking for something just a bit more substantial than a windbreaker.  

The Atom Hoody, Atom Jacket and Atom SL Hoody are all available at REI.com for those of you who are members of the co-op and like to earn your 10% rebate each year. 

How to wash your Atom Hoody

Arc'teryx recommends washing your Atom Hoody with Nu Down Detergent, and then using Nu Durable Water Repellent to reapply the DWR finish to your jacket. Here are step-by-step directions:

When to wash

• Heavy use (e.g. running, ski touring) – wash every 10 to 12 days of use

• Light use (e.g. dog walking, casual wear) – wash every 20 to 30 days of use

If your Arc'teryx jacket looks dirty or is no longer beading water, it’s time to give it a wash and re-apply DWR.

How to wash

• Close the jacket's primary zipper.

• Open the pocket zipper and ensure all items are removed. Leave the pocket zippers open.

• Release the tension on all elastic drawcords.

• Place your Atom in the washing machine and add cleaning detergent as indicated on bottle. 

• Wash on medium cycle heat (40C/104F) using a permanent press or gentle cycle setting. 

• Run a second rinse cycle to remove any residual soap. 

How to dry

• Place your damp Atom in the dryer on medium heat for 40-50 minutes. This will reactivate the jacket's DWR. 

• Re-apply DWR finish if needed. How do you know whether it's needed? Test your clean and dry garment with a light spray to see if water beads off the surface. If water is not beading off your jacket, re-apply a DWR treatment.

Arc'teryx does not recommend using a wash-in DWR treatment because it doesn't guarantee an even application over the entire surface of your jacket. Instead, use a spray-on DWR finish.