Arc Concept FAQ

The now widely accepted Arc Concept of ultralight sleeping bag design is unique to Nunatak Gear. Creating a quilt like cover, by eliminating zipper and hood, has proved to be the answer to both effective temperature control and remarkably light, compact bags.
Here answers to some of the issues a first time user might have:

These bags don't have hoods. How does that work?

It's definitely different from the standard mummy design. But then off course there's nothing standard about the Arc Concept. Sleeping without a hood is no problem if you have warm head wear along on your trip, and who doesn't? It puts that emergency balaclava or beanie to double use and will save you a few ounces, which is basically what this is all about. You can also use our super warm down filled balaclava for severe conditions, or carry a SkahaPlus, our ultralight hooded down sweater. It is designed to work with the Arc Concept bags for added warmth and versatility.

Does the sleeping PAD go inside the foot box?

No, the foot box will not fit around any pad on the market today, unless you cut down a Ridge Rest or something similar. Our foot boxes are designed for maximum thermal efficiency, which is best achieved with a snug fit. Trying to dimension the foot box to fit around a sleeping pad would sacrifice warmth and add several ounces in material and fill. We have tried bags that were meant to have the pad inside and found them to be too rigid and uncomfortable, akin to be back boarded on a litter.

Do I run the straps under the sleeping pad?

You can. It is one of two options, the other being as shown in the first picture on the right. With the straps under the pad you have more control over the sleeping bag when turning, but more air will be trapped inside making it the less warm of the two.

What kind of shelter do the Arcs work best with?

Bivvy bags and lightweight tents are our preferred shelters and the Arc line is designed with these in mind. Tarps work fine also, but on really windy and cold nights you have to work a little to eliminate the drafts.

What fabric should I choose?

Fabric choice is a compromise between breathability and moisture control. Tarp and bivvy bag users should consider leaning towards the water resistant end of the scale, since driving rain and condensation is more likely. If you mostly sleep in a tent, we think the choice is clear for the Quantum. Here's a link to our fabric page.

Are drafts a problem?

As mentioned above, if you're under a tarp on a cold and windy night you might feel some, especially if you toss and turn without doing the slight readjusting of the fit that is sometimes necessary.

Are these strange bags really warm enough?

All the sleeping bags in the Arc Line have a conservatively estimated temperature rating. If pushed beyond this they will eventually feel too cold. But if used correctly, wearing adequate head gear, they are comparable to mummy bags of the same rating.

How many custom options do I have?

Nunatak Gear is making every product to order, and that also applies to the Arc line. If our stock dimensions and features are different from your needs we will build your bag the way YOU want it. Call us to discuss the procedures.

What's the difference between all these models?

Even though they all share the Arc Concept as their design background, there are very clear distinctions between the individual models. First, they differ in temperature rating, from the 40 degree Arc Edge to the dedicated winter bag, the Arc Expedition. Following this increase in loft there's also a change in fit. You have more room in the warmer bags.

And which should I get?

Hard one to answer. Only you know your needs. We can say this much though: If you need the Arc Edge or the Arc Expedition you probably already know it. These two specialized bags are meant for the experienced back country traveler that realizes the products strengths and limitations. On the other hand, if you are new to wilderness travel or unsure about the Arc Concept, a good place to start is the Arc Alpinist.



Typical set up for mild conditions. Straps will likely be unbuckled and the bag is used merely as a cover. The feet can easily pass in and out of the foot box to further regulate body temperature.

Underside view in cold weather mode.
Straps are drawn tight and the snap fastener in the neck is closed. The elastic draw cord at the top of the bag is also tight, but can be accessed conveniently from the inside.

Bag and pad held together with the two sewn-on 3/4" straps. This set up is less warm than the first example, but offers more freedom to toss and turn.

Underside view with straps wide open and top snap and shock cord undone.
Foot box detail, underside view.  
Strap detail.  
Head opening detail with snap fastener and draw cord closed.  



Arc AT

Arc Edge

Arc Ghost

Arc Specialist

Arc Alpinist

Dual Arc Alpinist

Arc Expedition

Down Balaclava

Nunatak is dedicated to custom design and manufacture of quality back country sleeping bags and garments
utilizing 800+ goose down and sophisticated fabrics.

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