Sleeping out in the Nunatak Arc Ghost.
Publisher's Note: Variable girth bags have long been a part of BackpackingLight.com's history. The variable girth concept was the subject of BPL's very first editorial that was released prior to the launch of the site, way back in April 2001, before any variable girth bags were made available on the commercial market. We acknowledge BackpackingLight.com subscriber Don "Photon" Johnston, who was as instrumental as any individual in bringing the variable girth concept to market. Read more information about the history of the arc cross section variable girth design.
At just 14.9 ounces for a size long, the Nunatak Arc Ghost is among the lightest 32 °F (0 °C) rated bags on the market. It achieves this light weight through its simple, effective design: it features a closed foot box but an open, zipperless back. The back can be closed with two adjustable straps and a snap-closed neck with cinch cord, or it can be left open and used as a blanket. Not just lightweight, this "Variable Girth" design increases versatility, allowing the bag to be used within a wide temperature range by adjusting its circumference. A warm hat, hood, or balaclava is needed in colder temperatures as no hood is provided with the bag. The Arc Ghost is an innovative and well-constructed bag that is a good value, especially when considering its weight and versatility.
- Extremely light at 14.9 ounces (423 g) for size large
- A lighter weight and narrower version of the Arc Alpinist
- Warm enough for cooler temperatures when using a warm hat and extra clothing
- Two body straps and a neck snap and cinch secure the bag to your body
- Variable girth, can be cinched tight or unclipped and used as a quilt
- Foot box is warm but a snug fit
- Open back takes some getting used to, but is effective when sleeping stretched out on your back or stomach
|Small fits up to 5'4" (163 cm), Medium fits up to 5'10" (178 cm), and Large fits up to 6'4" (193 cm)|
|Backpacking Light measurement 14.9 oz (423 g) size large; Manufacturer specifies 16 oz (454 g)|
|800+ fill power goose down|
|9 oz (255 g) size Large (tested), 8 oz (227 g) size Medium, 7 oz (198 g) size Small|
|Backpacking Light measured single layer loft 2.25 inches (5.7 cm)|
|32 °F (0 °C)|
Outer And Liner Material
|0.85 oz/yd2 nylon with Teflon DWR|
|No (two adjustable straps and snap with cinch at neck)|
|$278 (small), $307 (medium), $340 (large)|
The Nunatak Arc Ghost uses a closed foot box, two body straps, and a collar snap with bungee cinch strap to hold in the heat.
The Nunatak Arc Ghost is a simple, effective, and extremely lightweight (14.9 ounces for size long) solution to sleeping in temperatures above freezing. It is a zipperless bag that has a closed foot box and an open body that insulates on the top and sides. During warm temperatures, the bag can be draped over you like a quilt. When the temperature gets colder the sides of the bag tuck underneath your body and two body straps cinch to secure the bag beneath you. This "Variable Girth" system allows you to adjust the circumference of the bag based on temperature or the amount of clothing worn inside the bag. The neck of the Arc Ghost closes with a snap and has an elastic drawstring at the center. It does not have a hood so a warm hat or balaclava is necessary in colder temperatures (Nunatak also has a separate Down Balaclava available for full head and neck coverage).
The Arc Ghost is sufficiently sized to fully wrap over my broad shoulders and the bag comes together at the back with about a 6 inch uninsulated gap with the straps fully tightened. It is designed to be used on top of a sleeping pad, unlike the Western Mountaineering Pod bags, which attach to the pad with straps, allowing the Nunatak bag to be closed almost completely. (While it is possible to attach the straps beneath a pad, this option is not as warm.)
Sleeping in the Nunatak Arc Ghost takes some getting used to. Rolling over as you might in a traditional bag exposes your back to the cold air. However, I quickly learned to hold the bag in place when rolling over to keep the bag from shifting with my body and it soon became second nature. While the bag works best for back sleepers, I am typically a stomach sleeper and the bag worked fine in this position as well. When sleeping on your side, it's difficult to keep the sides of the bag properly tucked under your body.
I never missed not having a zipper on the Arc Ghost; the strap system was easy to adjust and I had no problem getting into and out of the bag. If things got warm or I needed to get up quickly, releasing one snap and two small quick release buckles were all it took to open the bag completely. The two straps and top snap do a good job of keeping the bag evenly pulled under your body. However, there were times that gaps formed, especially when curled up. The main problem area was in the upper back between the top strap and the neck snap (a 29" space in size L). A third cinch strap would add a little weight but would help to avoid gaps for active sleepers like myself - especially in this larger size.
The bag is cut trim for a high degree of heating efficiency per ounce but there is sufficient room for me to wear insulated clothing inside and still have full coverage over my sides and shoulders.
The Arc Ghost provides plenty of coverage under my back, even with the straps loose.
In the field, the Nunatak Arc Ghost provides a similar level of comfort to other bags with a comparable manufacturer's temperature rating. However, it is difficult to fully turn over inside the bag without letting some cold air in. This bag is much better for back or stomach sleepers; those that sleep curled up on their sides may have a difficult time avoiding gaps under the body.
Without a hood, the Arc Ghost relies heavily on choice of headwear for warmth in colder weather. On one night when temperatures approached freezing (the bag's temperature rating), I slept cold because I only had a thin fleece cap. On later trips, using a warmer hat in similar conditions made the bag much more comfortable to use; a warm down or synthetic hat that fastens underneath the chin or a balaclava are essential when pushing this bag to its limit. A lightweight bivy also helps control drafts, increasing the bag's versatility. When the weather is warm, however, the hat and bivy can be left at home and you can sleep comfortably with the bag simply draped over your body. With the right combination of accessories for the conditions, I found the Nunatak Arc Ghost to be quite comfortable in a wide range of weather conditions. It is also among the lightest bags available at this temperature range.
The Nunatak Arc Ghost is constructed with rectangular baffles that are well-filled with 800+ fill power goose down and provide 2.25 inches of loft on the top. I experienced no problems with down shifting in the baffles during testing.
Missing from this review (and for all sleeping bag reviews published here, for that matter) will be an assessment of whether or not the sleeping bag performs adequately at temperatures near its manufacturer-reported temperature rating. Click here for the complete Backpacking Light Position Statement on Sleeping Bag Temperature Ratings.
The Nunatak Arc Ghost works well when sleeping stretched out on your back or stomach; it tends to leave gaps underneath when side-sleeping or curled up.
The Arc Ghost is a custom bag that is available in three different fabrics, a variety of colors, with overfill, or any other modifications you like (for an additional expense, of course.) The bag I tested used the 0.85 oz/yd2 nylon with Teflon DWR coating, which is the lightest fabric option available. Despite its weight, the fabric showed no wear during testing and only passed a couple of feathers. The DWR coating shed water easily and wasn't affected by many nights on the trail. Craftsmanship on the bag is excellent with seams folded in along the exterior edges for extra durability. The thin strap buckles did not break when stepping on them and with no zipper to jam, this bag should prove to be very reliable.
This is an extremely light bag that is well constructed and has good loft. At $259, $283, and $307 for size small, medium, and long, respectively, the Nunatak bag is not cheap but is competitive with other manufacturers. When you consider the versatility of the bag, it is a solid value.
Recommendations for Improvement
The changes I would like to see in the bag are:
- A third strap added to the bag, at least in the size long (this is available as a custom option)
- A lighter weight and less expensive hat/hood option for three-season use (the Nunatak Down Balaclava weighs 3 ounces and costs $99)