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Arc'teryx Sigma SL Anorak Review

The Arcteryx Sigma SL Anorak is a unique pullover softshell jacket that is an excellent layer for use in alpine environments
Arc'teryx Sigma SL Anorak
Credit: Arc'teryx
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Price:  $189 List
Pros:  Extremely lightweight, harness-compatible hem
Cons:  Anorak does not offer as much ventilation, can feel clammy during activity
Manufacturer:   Arc'teryx
By Ryan Huetter ⋅ Review Editor  ⋅  Mar 10, 2019
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  • Weather Protection - 30% 8.0
  • Breathability - 30% 4.0
  • Mobility - 20% 7.0
  • Weight - 10% 10.0
  • Features - 5% 3.0
  • Style - 5% 4.0

Our Verdict

The Arcteryx Sigma SL Anorak is a unique jacket to this review in that it does not have a full front zipper. Instead, it is a pullover with a half zipper for ventilation, a small chest pocket, and a hood, but otherwise is a very spartan design. Intended for use as part of a layering system while alpine climbing in harsh environments, the style is simple and elegant, though there do exist well thought out features such as a three-way adjustable, helmet-compatible hood and a Hemlock that keeps the hem secure under a climbing harness. This is a great choice for ice and alpine climbers who rarely need a full front zip, have a dialed layering system and are interested in incredibly lightweight and function-built gear.

Our Analysis and Test Results

We tested the Sigma SL Anorak during a week-long ski trip in the remote Selkirk Mountains of British Columbia. Weather conditions ranged from bluebird powder days to driving snow and winds, making it the perfect place to test.

Performance Comparison

Arc'teryx Sigma SL Anorak softshell jacket - this is a unique layer, and is the only pullover style softshell we...
This is a unique layer, and is the only pullover style softshell we reviewed.
Credit: Steve Mace

Weather Protection

In constructing the Sigma SL Anorak, Arcteryx used a proprietary material called Aequora Airperm, which sounds more like an aerosol hairspray than an ultralight and durable fabric. The tight weave of the shell fabric allows it to keep cold gusty winds from stealing away body heat, and we found that with only a thin merino base layer could stay comfortable and warm while being active in temps down to the mid-20s.

Arc'teryx Sigma SL Anorak softshell jacket - this jacket does a better job at protecting against wind and snow...
This jacket does a better job at protecting against wind and snow than rain, here you can see the soaking it got after only a short time in the shower.
Credit: Ryan Huetter

The Sigma SL provides adequate protection from water, though wetted out after only 5 seconds in the shower test. This is a jacket best suited for when precipitation is falling as snow, as it does not have nearly the same water resistance as the Patagonia Galvanized or even the Arcteryx Gamma LT.


The Sigma SL is light and made from rather thin material, and does a reasonable job at breathing well in most conditions that we tested in. The material itself lets moisture pass through, though, with the half zipper featured in this anorak design, we could not vent very easily, resulting in more of a clammy feeling inside during heavy exertion than we found in other models.

Arc'teryx Sigma SL Anorak softshell jacket - we appreciated the breathability of this softshell on more...
We appreciated the breathability of this softshell on more consistently paced climbs.
Credit: Steve Mace

This is not the jacket to take on a trial run, rather it is better suited for an activity such as alpine rock or ice climbing during which the pace is not as rapid and the need for lots of vents and zippers is outweighed by the need for mobility and lightweight.

Mobility & Fit

The tailored fit of the Arcteryx Sigma SL Anorak is a notable selling point of this layer. It felt true to size, was snug without feeling constrictive like the smaller than advertised Mammut Ultimate, and with ample panels and underarm gussets, we felt like we could freely move while climbing and hiking.

Arc'teryx Sigma SL Anorak softshell jacket - stretchy and nimble, this jacket moves well in climbing situations.
Stretchy and nimble, this jacket moves well in climbing situations.
Credit: Steve Mace

The elastane that is blended into the shell material makes the fabric incredibly stretchy, allowing us to feel unrestricted, which is necessary to this type of jacket since it is intended to be worn as an integral part of your layering system, not taken on and off as needed.

Weight & Packed Size

With a verified weight of only .65 pounds (10.4 oz), a spec that matches the manufacturer's claims, the Sigma is astonishingly lightweight. This is noticed while it is worn especially in warmer temperatures. While it is going to be on your back most of the time and not being carried inside the pack, its scant weight and grapefruit-size make it easy to stuff in the day pack as an emergency layer for a multi-pitch climbing outing for when the winds pick up and you need some added weather protection.


While overall simple in design the Sigma SL has a number of interesting and useful features that are driven by its intended use in climbing applications. The hood has three-way adjustable drawstrings and can be worn with a climbing helmet (though not a ski helmet). The innovative Hemlock keeps the hem tucked securely under a harness, a nice touch for those reaching high for that next hold or tool placement. There is only one chest pocket, large enough for a cell phone but barely.

Arc'teryx Sigma SL Anorak softshell jacket - the hemlock keeps the jacket securely in place under the harness.
The Hemlock keeps the jacket securely in place under the harness.
Credit: Ryan Huetter


This softshell is clean and simple in design and is available in three solid colors, but the fit and function of the jacket make it pretty clear you are either going out or coming back from a climbing mission. There is not much overlap with around-town style here.

Arc'teryx Sigma SL Anorak softshell jacket - light and fast in the range of light, a great place for this jacket...
Light and fast in the Range of Light, a great place for this jacket to shine.
Credit: Steve Mace


This is a specific, niche softshell jacket, but is a very well made one. This is a reasonable deal for a quality garment that serves a unique purpose in the wardrobe, but it is not a do-it-all softshell by any means.


We really liked the Sigma SL for its excellent mobility and movement, its durability and climbing-friendly features. The anorak style may not be appealing to all, but for those who need a form-fitted layer while out on a hard ice lead, this may be the answer you've been looking for.

Ryan Huetter
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