Arc UL Four Season

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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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A few things to keep in mind:

  1. We measure the actual width of the finished quilt without stretching. 
  2. The measurement is a minimum. 
  3. The differential cut makes the inside narrower than the outside.
  4. Adequate quilt width is the number one defense against cold inducing drafts. Our recommendations will get you a quilt generally wider than other brands with similar specs.

Appropriate use

The 10°F Arc UL is designed to provide sleeping comfort in the western US mountains from March to November.

The primary role of our warmest Arc UL is to help notoriously cold sleepers staying comfortable during normal 3 season high mountain backpacking. For some users it could suffice in mild winter conditions. However, it's still a quilt with the typical draft issues and potential mixing of inside/outside air while shifting and turning over. 

Planning to use any zipper less quilt on a prolonged winter trip is not a smart idea. Instead please consider the 3D Quilt.

Fill and Loft

The loft is a minimum of 3.25”  Fill volume is detailed in the chart, and offer further insight into whether this quilt will meet your needs.


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 10°F Arc UL is built with a permanently closed foot section of about 16" to 20" length 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.

Ultralight: 10d ultralight breathable shell. 

This ultralight fabric creates a comfortable sleep environment at the lowest weight. It will, however, wet out and transfer moisture to the down if exposed to prolonged dew, mist and damp tents. On the other hand, the superior breathability allows it to dry quickly in the sun. Ideal for moderately dry weather, desert hikes; or anywhere with a traditional double walled tent.

Classic: 15d lightweight breathable shell.

Nearly the same properties as the ultralight material above, but a significant increase in durability and tear strength. Expect a weight increase of up to 2 ounces, depending on size.

Full Moisture protection: 7d ultralight waterproof/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 7d wp/b is coated fabric, yet has a very light denier count, and as such adds under 5% to the total weight over the 10d option.

Combo of above two: A combination of 10d15d breathable and 7d wp/b shells. 

With 7d wp/b 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 additional articles with helpful pointers on selection and design:

Choosing the right Quilt

Quilt Straps and Cords

Designing with Down

Why Overfill?

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

Arc UL 10°F in the stock forest green 10d shell.


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



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Arc UL Four Season

Arc UL Four Season

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.

10°F / -12°C. Includes differential cut
Inside Length
To determine the correct length please refer to the measurements in the chart.
Shoulder Width
Measure around your widest part, including arms. Add 8-12” to this number for the best performance.
50" Our narrowest size for slim folks who doesn’t toss and turn much; and experienced quilt users wishing to save weight.
56" The most popular size that fits most frames.
62" For bigger people and/or those who toss and turn.
68" Very wide quilt - sprawling coverage!
Footbox Size Circumference
40" is the male size 10-11 shoe standard. For side sleepers the 40" is good to size 12-13
Shell Material

Two options: Ultralight 10d for the lightest, most breathable and best lofting performance. 15d for more durability and tear resistance with only a small weight penalty.

Waterproof/Breathable Shell Options

The first selection substitutes a black 7d waterproof/breathable shell fabric to the lower third of the quilt, plus the top neck/head opening. The large torso middle section remain with the classic 10d breathable fabric.
The second choice, represented by 'Full Coverage', will completely replace the 10d breathable material with a full coverage of the 7d waterproof/breathable shell in blue.

Liner Material Options
Choose between lightest - the 10d - or long lasting comfort at the penalty of several ounces extra weight: the 20d
Down Type

We use 900 fill power goose down, certified responsibly sourced.

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 untreated down.

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

Strap package

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

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. The amount depends on the product, the size and the rating.
No Thanks
Overfill in foot section
Overfill in torso section
Overfill evenly throughout
Optional Fully Integrated Apex Over Quilt

50°F synthetic filled Apex over-quilt providing a rating boost of 12-15°F. It is custom cut to fit over the Arc UL without compressing the down insulation, and provides 6-8 integration points to hold the two together. Average weight is 16-18 ounces. Black 10d inside and out with a sewn closed mummy style footbox. Drawcord at the top, ETC system.

No Thanks!
Yes, include a custom 50°F Apex over-quilt
Stuff Sack
Our stuff sacks are pretty dope, but current weight saving trends in ultralight circles eschews this once crucial item. So, opt out and save $ while also being very current.
No stuff sack
Yes, please include a stuff sack
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