Arc UL - 20°/10°F

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The Arc UL quilts are designed for optimal efficiency in the environments met by long distance hikers.

Custom features including sizing and weight saving options.

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Custom item. Multi week lead time.

Appropriate use

This Arc UL is designed to provide sleeping comfort in the western US mountains from April to late October, while balancing the modern hiker's demand for the lowest possible weight and bulk. 

In the menu you'll find two temperature ratings, realistically defined as either 20°F or 10°F. The loft is a minimum of 2.5" and 3.25".  Fill volumes for either level are detailed in the charts, and offer further insight into whether these quilts will meet your needs.

The 20° rated Arc UL is the standard go-to, do anything quilt. Our most popular choice for long-distance hikers ready to keep going towards fall.

The 10° rating of the warmest Arc UL is very conservatively rated. For some users it will feel even warmer and could suffice in mild winter conditions. However, it's still a quilt with the typical draft issues and mixing of inside/outside air while shifting. It's primary role is to provide abundant trail warmth for notoriously cold sleepers during normal 3 season high mountain backpacking.

For real cold weather use please consider the 3D Quilt.


The length is in 4" increments defined by measurements plus X-Small to X-Long descriptors. Using this system you can choose how far up the quilt reaches when on your back. In open mode reaching just the chin level is the absolute shortest anyone should go, and then only on quilts for the warmer seasons. Reaching the user's 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 toes.

The shoulder and foot area widths can be customized for individual needs and sizing. Newcomers to backcountry quilts can experiment with a blanket before committing to a sizing setup. 

Foot End Design

The Arc UL in 20° and 10° is built with a permanently closed foot section of about 16" to 20", depending on size, and then finished with a round bottom piece. A design common with high-end mummy bags.

Shell Material Choices

Immediate apologies for the complexity of the following! 

We offer the discerning user options to fine tune the performance of the Arc UL via a series of technical shell materials.

Basically there’s three distinct categories:

1: Classic breathable shell. 

These ultralight choices create a comfortable sleep environment at the lowest weight. They will, however, wet out and transfer moisture to the down if exposed to dew, mist and damp tents. On the other hand, the superior breathability allows them to dry quickly in the sun. Ideal for moderately dry weather, desert hikes and anyone with a traditional double walled tent.

2: Robic ultralight waterproof and breathable shell.  

With this as your outer material there’s minimal concern about external moisture migrating to the down. Also, the lesser breathability boosts the temperature rating a small amount.

The choice for wet environments, ‘cowboy camping’ and for users of flat tarps wanting to eliminate the bivy bag. The Robic has a very light denier count, and as such adds under 5% to the total weight over the Classic option.

3: A combination of Classic and Robic shells. 

With Robic only covering the outer foot section and top draft collar you can protect the down where it matters the most, while leaving the large mid section fully breathable. For use in the modern single wall tent where rampant condensation often collides with the lower end of sleeping bags. Also, the draft collar is protected from moist exhalations. A very versatile setup.

Look closely at the configuration table below, in order to select precisely what suits your use.

Liner Material Choices

The worst long term wear on quilt fabrics is the inside liner material. If you want to break with true UltraLight traditions, and risk adding up to 2 ounces (!!) of weight, the Arc UL can be upgraded to our soft, durable 20d Taffeta black liner, specifically developed for sleeping bags.


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.

We also have two brief articles with helpful pointers on selection and design:

Choosing the right Quilt

Designing with Down

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

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.

  • 1 out of 1 people found this review useful.

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 - 20°/10°F

            Arc UL - 20°/10°F

            The Arc UL quilts are designed for optimal efficiency in the environments met by long distance hikers.

            Custom features including sizing and weight saving options.

            Product Options
            Temperature Rating
            The rating reflects the lowest temperature during which a well conditioned hiker can expect to remain comfortable throughout a full night. Adequate shelter and ground pad must be used.
            20°F / -7°C. Includes differential cut
            10°F / -12°C. Includes differential cut
            Inside Length
            To determine the correct length please refer to the measurements in the chart.
            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.
            Footbox Size
            40" is the male size 10-11 shoe standard. Adjust accordingly.
            Shell Material Options

            These are the Classic breathable ultralight shell options, typically listed from lightest to most durable. 

            Please go to the Fabric Page for help choosing the shell material.

            Waterproof/Breathable Shell Options

            The top four in this selection applies a 7d waterproof/breathable shell fabric to the foot section, plus the top near the head opening. The large vertical baffled middle section remain with the material/color chosen in the previous field . Select colors to match - or not! The second choice, represented by 'Full Coverage', will completely replace all other shell choices with a full coverage of the same waterproof/breathable 7d ultralight shell.

            Liner Material Options
            Choose between lightest - the 10d - or long lasting comfort at the penalty of several ounces extra weight: the 20d
            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. A 5% increase in fill weight also occur.
            900 Fill Power Goose Down, RDS Certified
            900 Fill Power Goose Down, Hyper-Dry, RDS Certified
            Edge Tension Control

            This design involves two user adjustable shock cords running lengthwise along the left and right quilt edges. On cold nights tension the cords to shorten the edges and draw them under you; during milder conditions completely slacken the cords to have the blanket throw feel. Go here for more info

            No Thanks
            Yes, Include Edge Tension Control
            Strap package

            Straps snug the quilt around you and/or the sleeping pad. Go here for more info

            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.
            Down Overfill
            Adding overfill can prolong the life of the down, help maintain loft during moist conditions, boost the temperature rating by a small amount and keep the down volume from shifting. Expect a weight increase ranging from one to six ounces depending on the product, the size and the rating.
            Your Measurements
            Optional: Fill in the blanks to ensure getting the best fit. No changes will be made to your size selections without approval
            Shoe Size