First look: The 2025 Arc’teryx Proton SL Hoody

We've got great news for fans (and future fans) of Arc'teryx's lightest-weight version of the uber-comfortable, uber-versatile Proton insulated hoody: it's officially back for spring 2025. Now called the Proton SL Hoody (it was most recently named the Proton Lightweight Hoody and before that the Proton FL Hoody), it holds the title of Arc'teryx's lightest and most breathable fully insulated hoody. More on that later. But first:

Cost: $280 (available now on Arcteryx.com and REI.com)
Fabric: Fortius Air 20-denier nylon
Insulation: Octa Loft knit liner
Weight: 370g (men's medium)
Changes from previous version: Recycled Fortius fabric is supposedly more durable
Yays: Super comfortable, highly breathable, do-it-all layer for medium- and high-output activities in cool weather. Also looks and feels great for around-town wear. 
Nays: Price

Keep reading this review for full details and specs on the men's and women's versions of the revised Arc'teryx Proton SL Hoody. We also break down how the Proton SL compares to similar insulated pieces from Arc'teryx, including the Proton Hoody, Atom SL Hoody and Atom Hoody. We've separately explored the differences between all the jackets in the Atom and Proton lines. 

We're fans of Arc'teryx's Jacket Finder tool to help find the right jacket for your needs. 

Proton SL Hoody: Materials & Construction

Those of you familiar with previous generations of the Proton SL Hoody, including last season's Proton Lightweight Hoody and the Proton FL Hoody from years past, will recognize the fabrics and design of the spring 2025 model. The only real change from 2024 to 2025 is the use of recycled Fortius Air face fabric, which Arc'teryx says makes the latest version more durable than its predecessors. 

About that Fortius Air 20 - it's an air permeable 20-denier plain weave nylon praised for its durability and breathability. Arc'teryx also uses the Fortius Air 20 in the regular Proton Hoody as well as the recently revised Atom SL Hoody. Breathability aside, we love the Fortius Air for its soft, stretchy feel. If you've ever worn a Proton Hoody, you know what we mean. 

But things start to look different from the Proton Hoody and Proton Heavyweight Hoody when you take a look at the inside of the Proton SL. That's because its insulation is provided via Octa Loft knit liner, a lightweight polyester insulator that's soft against the skin while also having hydrophobic properties. Instead of absorbing moisture from, say, your body's perspiration, the Octa Loft pushes it away and lets the Fortius Air do its thing by passing that moisture through the face fabric and out to the exterior of the Proton SL. One more thing about Octa Loft: it maintains its loft and shape incredibly well, meaning you can stuff it in your pack as often as you need without real concern about its durability. 

Weather resistance

The Proton SL Hoody won't keep you dry in an extended downpour, nor should it. Its value is in its lightweight warmth and breathability, features that would be compromised by a Gore-Tex waterproof and windproof membrane. Like other members of the Proton family, the Proton SL Hoody is treated with a PFAS-free FC0 DWR (durable water repellant) finish, which helps precipitation bead up and roll away instead of soaking into the Fortius Air face fabric.

But DWR is only so effective, so while the Proton SL Hoody can absolutely tolerate light amounts of precipitation, be sure to pack a waterproof shell if weather is a concern. The Beta SL and Alpha Lightweight are excellent choices when weight and packability are a concern. The Beta AR, Alpha Jacket and Alpha SV Jacket are more rugged and durable Gore-Tex shells for four-season use or most extreme activities in the alpine. 

Learn more:

Beta AR vs Beta SL vs Beta: How to decide between Arc'teryx's most popular line of Gore-Tex shells

Alpha vs Beta: Highlighting the different use cases for each

Warmth & Insulation

As the only member of the Proton family - and the only Arc'teryx jacket period - that uses Octa Loft hung knit insulation, describing the Proton SL Hoody's warmth by means of comparison is difficult. But we can confidently state that the Proton SL Hoody is warmer than the Atom SL and not as warm as the regular Proton Hoody. 

With even a minimal baselayer, the Proton SL Hoody should keep you warm in temperatures as low as the 20s Fahrenheit - provided you're doing something aerobic that generates body heat. The Proton family was created to be breathable for medium- to high-output activities, and they serve that purpose incredibly well. They're not made, however, for keeping you warm while standing around in cold weather. Like many Arc'teryx garments, the Proton SL Hoody was designed with climbing in mind. And like many Arc'teryx garments, what works for one high-output activity also works well for many others. The Proton SL Hoody is a great jacket for cold-weather running, cool-weather hiking, ski touring and more. 

We mentioned earlier that the Proton SL Hoody is Arc'teryx's lightest and most breathable fully insulated hoody. The Atom SL, for example, is a lighter jacket, but it's only insulated through the body. Its sleeves and hood are essentially windbreakers. The Proton Hybrid Hoody, on the other hand, is insulated only in the front torso. All models of the Atom, including the SL, feature side stretch fleece panels that help with both movement and air circulation. We break down the differences between the Atom SL and the Atom for those of you considering which version best suits your needs. 

Fit & Feel

The Proton SL Hoody is "fitted," which is Arc'teryx's way of saying it's designed to function as a midlayer or outer layer. The relatively close-to-body fit works well for wearing the Proton SL under a shell, and it's roomy enough to accommodate your standard baselayer. 

It also features articulated patterning to encourage mobility and freedom - again, think of its stated purpose as a lightweight layer for Alpine climbing. 

Proton SL Hoody: Additional Features

Pockets

The Proton SL Hoody gets the standard Proton treatment when it comes to pockets - two zippered handwarmer pockets and an external, stretch-woven zippered chest pocket that's great for your phone, two-way radio or other communication device. The handwarmer pockets are positioned high enough on the jacket to remain accessible when wearing a harness. 

Hood

An adjustable, insulated hood is designed to be compatible with most modern climbing helmets

Zippers

The front zipper is a one-way Vislon zip that will work even if a tooth breaks.  

Cuffs

The knit cuffs are standard throughout the Proton line and do a commendable job of being comfortable and functional. They seal out drafts while still offering enough stretch to accommodate gloves both under or over the cuffs.  

Our take on the Proton SL Hoody

I love the entire Proton family of jackets. The Proton Hoody has been my go-to layer all winter long, with my Proton Heavyweight taking over on particularly cold outings. I wear them when I'm active and when I'm simply running errands around town. As winter shifts to spring here in the Colorado Rockies, the Proton SL Hoody will inevitably elbow its way into my regular jacket rotation. 

Its lightweight, breathable insulation and supreme comfort gives it Goldilocks status, as far as I'm concerned. If you're looking for a reliable and versatile performer in temps ranging from the 20s to the 50s, the Proton SL Hoody deserves a spot at the top of your jacket wishlist. It's going to provide more warmth than both the Atom SL and Proton Hybrid Hoody but also a little less weather protection, especially considering the Proton Hybrid Hoody's strategically placed Gore-Tex along the shoulders, arms and hood.