Arc UL Configuration Page

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The advanced Ultralight Series of Arc UL quilts are available in a wide temperature range designed with the lightest materials.

Custom features including sizing and weight saving options. 

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Custom item. Multi week lead time.


From this page all temperature ratings, sizing options and accessories of the Arc UL are configured

The Arc UL quilt is a specialists' tool, with lowest weight and bulk as the guiding design parameters. Features, functions and materials are all dialed in to meet the UltraLight goal.

Temperature Ratings

The Arc UL is available from a 30°F summer style quilt all the way down to 5°, in steps geared to fit the most useful seasonal applications. By far the most popular all-round rating is the do-it-all 20°.


A five step measure of the inside useful length in 4" increments is used parallel to the subjective and sometimes confusing Small to X-Long moniker. Using this system you can choose how far up the quilt reaches when lying on your back. Reaching just the chin level is the absolute shortest anyone should go, and then only on quilts for the warmer seasons. Forehead is the best compromise of low weight - efficient coverage.  As always, it is prudent to size up if in doubt. If just a little too short one tends to compress the foot area insulation to the detriment of cold feet.

Furthermore the shoulder and foot area widths can be customized for individual needs and sizing. Typically a 2 season quilt can be built a little narrower than a winter oriented set-up. If you're new to backcountry quilts, experiment at home with a blanket before committing to a sizing setup. 

Foot End Design

The Arc UL quilts are offered in two foot box configurations, also in the menu below. The traditional Arc design is a 20"-24" permanently closed section finished with a round bottom piece sewn in place. In other words, a sight familiar from high-end mummy bags.

The Vector foot end is a modular concept that allow the user to switch from closed to blanket style open foot area in a few simple steps. This option, while very adaptable to changing conditions, lack a little in thermal efficiency compared to the regular Arc. It also adds some weight, for those who count every gram. A page with a few pics detailing the foot box options is here.


The Arc UL is built with the lightest fabrics we have been able to source.

When using materials as thin as the unique Membrane .66 and Quantum equivalents, some compromise in durability and longevity must be anticipated. Generally though, in the hands of experienced users, normal life spans can be achieved with proper care.

In our experience the worst long term wear on quilt fabrics is the inside liner material. If you want to break with the true UltraLight tradition, and risk adding up to several ounces (!!) of weight, the Arc UL is also available with our soft, durable 1.0 Taffeta black liner, a fabric specifically developed for sleeping bags. Again, this adds weight that is described in the charts below! 

Upgraded weather resistance

The Arc UL can additionally be configured with a shell fabric exhibiting considerable weather/moisture protection. In the Shell Fabric menu below this is the Robic. Certain extreme environments will more than justify the increased cost of this upgrade.

Even for the user expecting less arduous conditions, the Robic will help dealing with the damp night time environment inside modern single wall UL shelters, or dew from sleeping under the stars.

Here's a brief description of this material

0.74 oz/yard Robic Ripstop Nylon: Extraordinarily light, this 7D fabric is treated with a microporous PU coating on the inside and a solid DWR application on the weather side. The ability to hold out moisture is very good with a HH of 1000mm. Breathability rating is adequate for down products. For a fabric with a square yard weight of well under an ounce, the Robic is relatively durable, edging out the highly breathable Membrane/Quantum shell also offered.


Besides the custom sourced shell and liner materials, we also consider shock cords, buckles, snaps and other notions as specific targets for UL optimization, further shaving grams. 

What's in the box?

The quilt, a set of quilt straps, a silnylon stuffsack and a large breathable storage sack.

Go to the bottom of this page for the full Arc UL Configuration Menu!

Temperature Ratings Available30° - 20° - 15° - 5°
Length and width choices affect fill weight by roughly ½ to 1 ½ oz, depending on temperature rating.

After saving your customized product, remember to add it to your cart.



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The Comforter!

I purchased this quilt, specced to 15 degrees with ultra wide dimensions (78" long x 66" wide) and a great big footbox too (45"). Super roomy for me or plenty to share with a significant other who doesn't have their own nice backpacking gear. I used it on an Arizona Trail thru hike in the Spring of 2017 with nighttime temperatures down to 15 degrees F, and will use it again next year for a CDT thru hike that will entail all kinds of snow and freezing temps. It's enormous, and excessive, and I love it. I call it the Comforter.

Even as excessive as I asked for it to be built via the awesome customization offered by Jan and Nunatak... this 993 gram (35 oz) Comforter (essentially a couple's thru hiking bag), only weighs 2 more ounces than a WM Alpinelite 20 degree in long (33 oz). It's a little bulkier in my bag, yes, but that bulk equals pure warmth, not unnecessary zippers. It's my great big security blanket against the cold windy mountains and snow, and I feel fine. Many thanks for an excellent piece of gear.


    Arc UL

    Review from March 2016, reprinted with author's permission:

    I have now used my quilt for 7 nights in South West Tasmania. It was excellent. Conditions were not that cold (4 deg C) but it was super warm and comfortable. Lumpy down from shipping dissipated. I even felt sorry for my friend who had a regular bag. So - I am very happy with my purchase.


      New quilt day!

      This review from 04/27/2016 is an excerpt from an email we received, and published here with the author's permission. Nunatak Admin.

      I received the quilt yesterday. First things first - I LOVE THE QUILT. There are very few possessions I own that I would never part with under any conditions - this quilt is already 1 of them. 1. The craftsmanship is superb - better than the Specialist I have. As good as western mountaineering or Katabatic. 2. You are properly filling your shells - I feel the shells were underfilled during Tom's ownership. No need for overfill whatsoever. 3. the 2" differential cut is perfect ( I wondered if 4" would be better). This is the most comfortable quilt/bag I've ever experienced. 4. I love the color (I was not expecting to like it) - your photos online are very accurate representation. 5. You delivered in 4 weeks! 6. The drawstring in the middle of the neck baffle is SUPERB - supreme comfort. 7. Footbox is generously filled and baffled. 8. You delivered right on the weight I was expecting - exactly 1lb 10oz (I had to extrapolate from your published numbers) 9. You sent along stickers and a "Birth Certificate" for the quilt. 10. I love the 20 degree so much I may sell my specialist instead of modifying it and purchase a vector from you for summer nights. Ian

      • 1 out of 1 people found this review useful.

      New 2 Season Arc Quilt

      From an email we received:

      I purchased my quilt summer 2016 and have used for ~ 20 nights since. It is considerably warmer than the three season (UK) bag it replaced while also being ~ 30% lighter - a testament to the excellent design and materials. The flexibility and comfort of the quilt it not undersold and I intend to take it trekking in Greece this spring where I will be sleeping at elevations between sea level and 2500 metres. No signs of wear and tear so far. Good service and delivered well ahead of original estimate. No reservations about ordering from Nunatek again.

      Kind regards,

      Jon Ball

      • 1 out of 1 people found this review useful.

      Arc 15F

      I ordered a Vector Arc 15 degree bag/quilt. Jan helped me modify the Vector so it opens completely as a quilt and the foot box closes completely with a cord acting as an arc. I added the weather resistant Epic shell with 900 plus fill down and added down insulation. Jan recommended a few inches be added to the Arc. I've used this bag indoors and outdoors every night for the last 6 months. It is perfect as a quilt inside and is wonderful inside a Gortex bivy outside. If you wear a down hooded jacket inside this Vector you will be comfortable in winter conditions. I love it and keep it with me wherever I travel in Oregon. It could be a life saver for me and my wife if we ever ran into a situation where we were stuck in winter conditions. Jan is always helpful whenever I have any questions. Customer service is awesome.


        32 deg Quilt

        After a long day on the trail I see myself dreaming of climbing into my quilt with its ultralight (15.8oz), ultrasoft feel, snugging around my shoulders. I have been cosy and warm in all conditions down to -1C so far and it is my number one sleeping option. Thank you Jan for your advice in helping me choose the right one for me.


          This Quilt will set you FREE

          I purchased my Arc UL quilt about a year ago and have nothing but high praise for it. I've used the bag for 55 days of hiking in Alaska, 40 days in the Grand Canyon, and a week of hithhiking/trainhopping in between. The quilt has been soaked, dragged, stuffed and generally abused constantly, and does not show a single sign of wear. It is insanely warm (20 degree), unbelievably warm, and ridiculously compact. Nunatak could charge twice as much for these wonders and it would be worth every penny. Do yourself a favor, buy one and never worry about a cold night again. Thank you for the worlds lightest mobile home Nunatak!


            Quilt & Jacket

            Review from 05/05/2016:

            Jan, The quilt and jacket arrived safely at my door step. Never have I received so large a box weighing so little, and with such wonderful things inside. They are absolutely perfect. Thank you so much for your excellent work. I really appreciate it. -Niles

            • 1 out of 2 people found this review useful.


            Review from 07/26/2016:

            Loved that Arc quilt in Colorado !! Getting the Nano quilt for the JMT - you guys are great . Thanks !!

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              Arc UL Configuration Page

              Arc UL Configuration Page

              The advanced Ultralight Series of Arc UL quilts are available in a wide temperature range designed with the lightest materials.

              Custom features including sizing and weight saving options. 

              Product Options
              Temperature Rating
              The all time most popular choice is the versatile 20°F.
              30° is considered a 2 season rating, while 5° qualifies for light 4 season use.
              Inside Length
              The useable length measured from inside the footbox to the top hem, without compromising the insulation loft. For example, if you're 6' tall and want the quilt to reach near the top of your head, choose 70".
              Shoulder Width
              54" is a good standard for regular sized folks who doesn't toss around too much. For winter bags go one size up.
              Foot End Style
              The Arc is the well known enclosed footbox sewn with a rounded bottom piece.
              The Vector gives you the option of opening up the quilt's foot area to a blanket style appearance. This comes with a slight compromise in thermal efficiency and about an ounce weight (30g) increase.
              ARC. Permanently Enclosed Foot Box
              VECTOR. Convertible - Blanket to Enclosed
              Footbox Size, Arc & Vector Models
              40" is the male size 10 shoe standard. Adjust accordingly.
              Shell Material Options
              Custom colors and qualities for the Arc UL
              Liner Material Options
              Choose between lightest - the Membrane - or long lasting comfort at the penalty of several ounces extra weight: the Taffeta
              Down Type
              Choosing Hyper-Dry moisture resistant down will help combat the effects of perspiration, misting tents and damp air. Nunatak products made with Hyper-Dry down will have a slight increase in bulk over those made with regular down. In some instances they may contain an additional 5% of fill weight.
              Down Overfill
              Cold sleeper? Consider adding a few ounces of extra fluff.
              Strap package
              Straps snugs the quilt around you and/or the sleeping pad. Options are: None (really?), ultralight shock cord style controllers, or the fully featured standard ¾" strap package.
              Gamut Climashield Over-quilt Compatability
              This mod makes a future over-quilt application as effective as possible. It adds snap buttons in the places needed, plus stores a record of your product's finished measurements and attachment points.