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.
Arc'teryx Sigma SL Anorak Review
Compare prices at 2 resellers Pros: Extremely lightweight, harness-compatible hem
Cons: Anorak does not offer as much ventilation, can feel clammy during activity
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.
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.
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.
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.
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.
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.
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