I've been publishing in-depth helpful guides to almost all Arc'teryx jackets for more than two years now (see full post list at the bottom).
Now that the summer is here, let's take a look at how the differences between Proton FL vs Atom SL play out.
Atom SL (Super Light) and Proton FL (Fast & Light) are the two most breathable, least warm alternatives you can find in Arc'teryx's insulated jacket line-up.
They're both best suited for chilly summer and/or spring mornings, followed by a high output activity (primarily rock / alpine climbing).
These jackets are more alike than they're different.
- Proton FL is slightly warmer, slightly more breathable, slightly more durable and comes with an inch longer hemline
- Atom SL is more wind resistant
Short answer is that unless you'll be using the jacket under windy conditions 90+% of the time, I'd probably recommend you to get the more versatile option, the Proton FL.
Neither of these jackets will provide substantial warmth. Like I clarified earlier, they aren't even designed to do so anyway.
Proton FL is insulated with Octa Loft throughout the entire jacket. The Atom SL, on the other hand, is insulated with Coreloft Compact only around the core, which holds it warmth back.
I'd recommend you to take a look at the lowest temperatures they're expected to be worn comfortably by an average person (both are positioned at the bottom):
Find below the lowest temperatures you can wear each jacket without feeling uncomfortably cold.
These are only approximate values assuming:
- you only have a shirt under and no shell over,
- during daily use (strolls, power walks etc at most - no high output activities),
- with light wind,
- and when it's dry out.
°F / °C
Arc'teryx LEAF Cold WX Parka SVX (Men's)
Arc'teryx Ceres SV (Men's)
Arc'teryx Dually Belay Parka (Men's)
Arc'teryx Thorsen Parka (Men's)
Arc'teryx Centrale (Women's)
Arc'teryx Piedmont (Men's)
Arc'teryx Therme Parka (Men's)
Arc'teryx Camosun Parka (Men's)
Arc'teryx Radsten Parka (Men's)
Arc'teryx Macai (Men's)
Arc'teryx Andessa (Women's)
Arc'teryx Patera Parka (Women's)
Arc'teryx Alpha IS (Men's)
Arc'teryx Radsten Insulated (Men's)
Arc'teryx Kappa (Men's)
Arc'teryx Sensa Parka (Women's)
Arc'teryx Magnus Coat (Men's)
If you think you run warmer or colder than the average person, then shift these temperature ranges accordingly.
See the performance ratings of these jackets too: https://outdoorcrunch.com/arcteryx-wiki/
Although Atom SL is the most breathable unit in the Atom line, Proton FL still breathes more.
Water, wind and abrasion resistances
While neither are comparable to outer layers (shell or belay jackets) at all, they'll fill the bill for spring and summer activities.
They're comparable in terms of water resistances, but Atom SL (Tyono 20) offers a slightly more wind resistance and slightly less abrasion resistance compared to Proton FL (Fortius Air 20).
They're both DWR coated.
DWR is a coating.
It's basically sprayed on to the surface of these jackets as a finish. It stands for Durable Water Repellent - which means that water will be repelled under wet conditions instead of soaking into the fabric.
DWR also decreases dry time.
It's a good thing these jackets are coated in DWR, but pay attention to the fact that DWR is a coating - meaning that it will wear off over time.
Which is why you might want to invest in a DWR spray such as this one for after treatment.
As you see, there's a strong correlation between FP x FW and temperature ratings, but not more than, say, 80%. I explained why this happens here in this post of mine.
Fit and size measurements
For a small size Atom SL:
- Chest width: 107 cm
- Shoulder length: 16.4 cm
- Waist width: 98.4 cm
- Front length: 67.3 cm
- Center back length: 71 cm
For a small size Proton FL:
- Chest width: 109 cm
- Shoulder length: 14.8 cm
- Waist width: 101.0 cm
- Front length: 75.7 cm
- Center back length: 75.7 cm
Both offer a trim cut.
I'd probably get the Proton FL. It's more versatile.
A helpful video review: