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Nunatak Arc Alpinist

Nunatak Arc Alpinist


by Don Johnston and Ryan Jordan | 2002-07-04 03:00:00-06

Ryan's Nunatak Arc Alpinist, Grand Teton National Park, WY


Nunatak Gear of Seattle, WA makes an innovative down sleeping bag called the Arc Alpinist. The "stock" model (6'0" length, 10" baffle spacing with 10 oz of 800+ fill down, 0.85 oz/yd2 shell and lining fabric) weighs a paltry 18 oz and has a manufacturer-claimed temperature rating of 20 deg F.

The Arc Alpinist is unconventional in design. While the bag has a mummy shape, it is manufactured more like a quilt. The bag has buckles and straps at the outer edges that transform it from a quilt into a nearly closed sleeping bag. Designed to be strapped underneath a sleeping pad, the Arc Alpinist's straps and buckles when tightened seal the sleep system against any drafts when the bag is closed.

The Arc Alpinist fills a unique niche: to provide maximum comfort in a very wide temperature range for minimum weight. Do you know of any other 18 oz bag with its temperature rating or flexibility over a wide range of conditions?

Ryan likes to refer to the Arc Alpinist as a "variable-girth" sleeping bag. Unbuckled and draped over him like a quilt, his custom Arc Alpinist (with 6" of loft, weight 21 oz) remains comfortable even on very warm nights (near 60 degrees). With its straps buckled and cinched tight (resulting in very little wiggle room), his Arc Alpinist is warm enough for a 15 degree night. By adjusting the straps and increasing the girth, Ryan can make himself comfortable in virtually any temperature between 15 deg F and 60. He can also increase the girth to accommodate extra layers, such as a down jacket and pants. In this configuration the Arc Alpinist is an ultralight winter sleeping system. Ryan has successfully used this approach to temperatures near zero degrees.

The Arc Alpinist has no hood, zippers, draft tubes, watch pockets, or other extraneous features that can add weight without significantly increasing performance for the summertime backpacker.

At $260 to $340+ (depending on size, fabric choices, and degree of customization), the Arc Alpinist is not cheap. But with well-selected custom options including both shell and lining fabrics (from among Pertex Microlight, EPIC, and 0.85 oz/yd2 nylon); specified loft or fill weight; and custom dimensions, it may be the ideal core to any ultralight backpacker's sleep system.

The centerpiece of this review is an analytical discussion between Don Johnston and Ryan Jordan about the design and performance of the Arc Alpinist - in particular their experience with the custom bags they ordered in 2001. Collectively they have used these bags on more than 100 backcountry nights.

Product Design

Don: I wanted a sleeping system for summer use wherever I might go, including mountainous areas of the US, where temperatures can drop to freezing. I wanted the bag to weigh as little as possible for that level of warmth, something like a Rab Carrington Elite Top Bag, only better.

Ryan: I was looking for simplicity -- a bag with an extremely wide comfort range that could, when combined with down or synthetic fill clothing as necessary, be used for both the zero-degree nights of a Montana winter and 50-degree nights on the Appalachian Trail.

Don: Like the Rab Elite, the Arc Alpinist is a "top bag" design. That is, there is no down on the bottom of the bag. Your sleeping pad serves as the bottom insulation. A closed foot box and a set of buckles and straps close the bag into a typical mummy configuration. When the straps are left unbuckled, you can drape the Arc Alpinist over you as a quilt. This bag/quilt feature is the core of the unique design that provides such a wide temperature range. In addition, with this bag/quilt, I have the freedom to sleep in any position I want (just like in a regular bed) within the limitation of the width of the sleeping pad and the foot pocket girth. For active sleepers like me, the straps can be secured underneath a sleeping pad, providing draft-free warmth with enough room to roll around, sleep in a fetal position, or just bring one knee up.

Ryan: I am convinced that remaining somewhat mobile through the night leads to a better nights' sleep. Moving around promotes blood circulation that heals tired legs and prevents the cramping that is common after extremely long and exhausting days on the trail or on moutain climbs. The variable-girth system of the Arc Alpinist is the key for remaining mobile during the night.

Don: In warm weather I don't use the straps. In colder weather I will strap the waist strap under the pad and use the neck adjustment as needed. For maximum warmth I will strap both straps, waist and upper back, under the pad, and I'll cinch the neck. This configuration lets me roll around inside without being exposed to drafts.

Ryan: I had a third strap added to my bag. The third strap that I added near the neck keeps the bag in a more closed configuration and retains more warmth. The reason was simple: I don't like to strap the sleeping bag under my foam pad, but I do like it strapped together. Because I tend to wear a lot of clothing to bed, I prefer to be able to control the degree of drafting that comes into the bag. Cinching the straps under my pad prevents this.

Don: I like the fact that that the Arc Alpinist is a hoodless bag. In warmer temperatures a hood is unnecessary, so why bring it? As temperatures fall, you can wear your balaclava or warm hat, something you already have as clothing anyway. If you want to push the bag to lower temperatures, you can switch to a down hood. This down hood would replace other warm headgear in waking hours and would serve as the hood for the sleeping bag. Excellent down hoods are available from Nunatak.

Ryan: I too had Nunatak make me a down hood. It's made with an EPIC shell and Pertex Microlight lining, has a loft of 3" and weighs 3.5 oz. I use the hood whenever I'm expecting average temperatures below freezing. The down hood seals drafts at the neck and is vital to pushing the Arc Alpinist comfortably down to temperatures less than 20 deg F. For most summer backpacking, where I don't expect temperatures below 40 degrees, I find that my wool watch cap provides plenty of warmth.


  Don Ryan
Size I am 5'7" 145 lb and I wear small or medium size men's clothes. This bag is sized to fit me but other sizes are available and it can be ordered custom-sized to your needs. I too am 5'7" but pushing 155 lbs. My typical clothing size is medium. My bag is custom sized (both length and girth). From my measurements, I suspect that it is about three inches shorter than the stock medium model.
Baffles My bag has a baffle height of 2.5 inches and a baffle width (spacing) of 5 inches. Nunatak's standard version has a baffle spacing of 10 inches, but I suspect that a 5-inch spacing increases down control and prevents shifting. I also specified a 5" baffle spacing. I suspect that this adds an ounce or so of weight. I specified a higher baffle height of 3.0 inches to accommodate the greater amount of down in my bag.
Fabric Since I was looking for minimum weight, I specified that 0.85 oz/yd2 fabric be used for both the shell and lining fabric. I prefer the shell fabric to be as breathable as possible to prevent condensation. Since I spend a lot of time in sub-freezing conditions, my shell fabric choice was Pertex Microlight (1.3 oz/yd2). My lining fabric is 0.85 oz/yd2.
Loft & Fill I specified the amount of down fill to be as much 800+ fill down as possible to bring the bag to a total of 18 oz. This end result was about 2.5 inches of loft. I specified my loft (3.0 inches) rather than fill weight. My bag ended up at 21 oz, 3 oz heavier than Don's, due to more down, an extra cinch strap, and slightly heavier shell fabric. I also specified that Nunatak use a differential cut between the shell and lining fabrics. This maintains full loft at the sides when the bag was cinched. This was a custom request.


Don: Operating the buckles and straps required a mental adjustment and a little practice. If I expect cold conditions, I will strap the waist strap under the sleeping pad before I get in and pass the other strap under the pad at the same time. If I need the upper strap I buckle it next and then clip a final buckle at the neck. When fully strapped to the pad I find it easiest to snap the buckle at the neck of the bag when on my stomach or by scrunching down in the bag and fastening the buckle with it held over my face then ducking under to get my head through. Once in and fastened down, I cinch the draw cord as needed. Alternatively, I can buckle everything and wiggle into the bag from the top and then cinch the neck.

Ryan: I don't like wiggling around, so I prefer to buckle the straps after I get into the bag. Sometimes this requires a bit of convoluted movement, which was frustrating at first, but when I realized that it demanded enough effort to generate some heat, I actually began to look forward to the ordeal. Seriously though, you get used to it, and it becomes second nature. I can clip/unclip buckles and adjust straps without thinking whether I am on my back or stomach.

Three Season Performance:

Don: On a five-day trip in the Tetons in September, I was comfortable in a thin nylon shirt and silk weight boxers, even on the coldest night, when my thermometer read 36 deg F. Humidity in the Tetons is low. (At home in my back yard I felt much colder in the bag at the same temperature but at 100% humidity.) I slept comfortably in my Arc Alpinist on a winter weekend in Pine Grove Furnace State Park. Both nights had temperatures in the low 20s. Conditions were dry with no wind. I slept in my Nomad 2-4-2.

Ryan: My Arc Alpinist has about half an inch more loft than yours, Don. I would also agree that it's comfortable (not just survivable!) in the mid-30s in only long underwear. With my normal 3-season clothing (which includes a light down or synthetic-fill jacket, thin wool top and bottom long underwear, a wind shirt, and rain shell jacket and pants), I am comfortable well into the 20s. However, to remain comfortable consistently after a difficult day of hiking on a 20 degree night (the claimed temperature rating of the stock bag, which has less loft), I would add a bit more insulation, such as a layer of Powerstretch fleece top and bottoms, or maybe just a pair of lightweight down or synthetic-fill pants. I have also experimented with down half bags (like Nunatak's Akula) and ultralight liner bags (including the 14 oz Western Mountaineering LineLite) and have found that this combination can easily push the comfort rating of the Arc Alpinist to zero degrees or less.

Don: When temperatures are expected to be below 30 deg F, I carry more layers of clothing. With my other conventional sleeping bags, I could not gain much more warmth wearing additional clothing in my sleeping bag. The bags' narrow girth compressed both the clothing's loft and the bag's. The only way around this was to use the bag as a quilt, which created a lot of drafts and defeated the attempt to get warmer.

The Arc Alpinist avoids these problems. The Arc Alpinist is spacious and as comfortable as a quilt in warmer weather. However, when the temperature drops, I can strap it to my sleeping pad. In this configuration it still has enough room to accommodate a lot of extra clothing. I've had the opportunity to use the Arc Alpinist in combination with my normal hiking clothing in temperatures near its claimed temperature rating of 20 deg F. In short, I'm comfortable with the Arc Alpinist without making changes to my normal clothing system.

Ryan: The beauty of the Arc Alpinist's design is its flexibility. It can accommodate virtually any combination of clothing between utter nakedness and winter down clothing. Barring an expedition to Denali or Borneo, I cannot imagine a bag that can cover such a wide range of conditions in comfort.

Cold Weather Performance

Don: Last summer I used this bag for a number of warm nights around home, on some local weekend trips, and for five days on California's Lost Coast trail. My bag arrived in the summer; so, lacking cold weather for testing, I did some testing in a walk-in freezer at work. This 20-degree-rated bag/quilt was never intended for the 0 deg F temperatures in this freezer, but finding temperatures cooler than the upper 50s around here (Maryland) in the summer was not an option. The freezer tested the bag well below its rating.

For this extreme cold I collected the clothes I would have along if backpacking in winter where temperatures might go this low. The Arc Alpinist has enough space inside to wear these extra layers of clothing without compressing the bag's or the clothing's loft. On my upper torso I wore my PHD Minimus down jacket and vest, a Patagonia Zephur jacket (which serves as a long underwear layer) and a button-down cotton shirt that I happened to be wearing to work. I wore my hiking shorts, Patagonia Zephur pants (long underwear layer), and my regular backpacking socks on my lower body. On my head I wore a pile balaclava pulled up to cover my lower face and nose to keep my nose from freezing, a Patagonia Pile Balaclava as well, and the hood from an old Patagonia Down jacket. I also wore Manzella thermostat dot gloves. I was comfortably warm at -4 to +4 during this test and dozed off but was watchful about my feet. They did not have enough insulation for the cold temperatures. My toes got cold after 2 hours. By then, I felt I had enough information to know I could sleep at 0 deg F if I had enough insulation for my feet.

Ryan: My coldest-weather experience differed a bit from yours, Don. I spent the night in a poorly-designed snow cave on a late January night in Montana's Bridger Mountains. I slept on a full length Cascade Designs Deluxe Ridgerest pad, which was inside an Integral Designs Endurance Bivy Sack. The Arc Alpinist was not strapped to the pad, but its straps were cinched tight enough to provide little wiggle room but not so tight as to compress my clothing. I wore my Nunatak down hood over a Powerstretch balaclava as headgear, a GoLite Coal Parka over Smartwool long underwear on my torso, lightweight merino wool tights and Schoeller Dynamic pants on my legs, and down booties over wool socks on my feet. At the near-zero temperatures inside the snow cave, and with very wet clothing and inadequate insulation for my legs, I pretty much enjoyed the night on the fringe of hypothermia. My saving grace was a 3L Platypus Big Zip water bottle that I filled up with hot water at 3 am to get me through the rest of the night.

Had I brought with me my normal suite of winter clothing, which would have included a down jacket and pants, I would have been fine with such a light sleeping bag. In another cold- weather test a few weeks later, I was able to confirm that the Arc Alpinist was indeed comfortable with just such a clothing ensemble.


Don: Based on my experience so far this bag is extremely versatile. For three-season use it will be my only bag. At 18.4 oz that is amazing.

Ryan: Ditto. Other than my McHale Sub-POP pack, the Arc Alpinist is the only piece of gear that I cannot imagine parting with in the near future.

Recommendations for Improvement

Any changes to the design (e.g. smaller baffles, a differential cut, more down, etc.) can be specified (for a fee) by the customer. So if you want to make your own design changes, go ahead and let Nunatak know. This is the kind of service that you simply cannot get from a major manufacturer. The downside to this: there will be a waiting period. Nunatak is a busy company with a small workforce; so do not expect to receive your custom bag for several weeks (possibly months?) after placing your order.

Final Grade A

We do not think we could give "A" grades to the stock Arc Alpinist as specified on Nunatak's web site, or we would not have had a need to order custom bags. However, the custom bags that Nunatak delivered to Don and Ryan certainly do rate an "A." The product is a winner.

Nunatak Gear (Seattle, WA)
2716 39th Avenue SW
Seattle, WA 98116
1-866-NUNATAK (686-2825)
Manufacturer’s Website:


"Nunatak Arc Alpinist," by Don Johnston and Ryan Jordan. (ISSN 1537-0364)., 2002-07-04 03:00:00-06.