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MontBell UL Spiral Down Hugger Sleeping Bag Review

A lot to like and a great value for a 30 F rated down mummy bag weighing only 19 ounces.


Overall Rating: Recommended

MontBell’s new Super Spiral Stretch System and soft 12 denier Ballistic Airlight fabric set a new standard for making a lighter sleeping bag. The bag is sized well, has a great fitting hood that is easy to operate, the zipper doesn’t snag, and it’s a great value. The superlatives are offset somewhat by the bag’s only average warmth and a stuff sack that is too small.

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by Will Rietveld |


MontBell UL Spiral Down Hugger #3 Sleeping Bag Review - 1
The Spiral Down Hugger #3 introduces MontBell’s new Spiral Stretch System and 12 denier fabric, which together reduce the weight of a sleeping bag by 2 ounces.

Like MontBell’s existing Super Stretch System, their new Super Spiral Stretch System is unique. Basically MontBell found an alternative way to create a stretchy sleeping bag and save some weight to boot. The technology is best described in their own words: “New for 2009, MontBell has incorporated a classic tailor’s technique to address sleeping bag comfort issues. By integrating a woven fabric 'cut on the bias' and orienting the fabric’s warp and weft threads at 45 degrees to major seam lines, the sleeping bag becomes more fluid or elastic in nature. Additionally, 'spring like' crimped fibers are used in the weave of the fabric to capitalize on their inherent stretch properties.” Rather than the traditional horizontal or vertical orientation of the down tubes, they are oriented on a 45 degree angle and appear to spiral around the sleeping bag.

The new Spiral Down Hugger line also introduces MontBell’s new 12 denier Ballistic Airlight sleeping bag fabric. Switching from 15 to 12 denier fabric plus spiral construction reduces the weight of a sleeping bag by about 2 ounces. Apparently MontBell is very satisfied with the new technologies because they intend to extend the Super Spiral Stretch System across their entire sleeping bag line (available March 2010), replacing the current Super Stretch technology.


The main features of Spiral Down Hugger #3, rated at 30 F, are its spiral construction, 12 denier fabric, 800 fill power down, sculptured hood, and three-quarter-length auto-locking zipper. The manufacturer claimed weight is merely 19 ounces for size Regular and 20 ounces for size Long.

My initial reaction to this bag is: “How did they do that?” Frankly, I don’t know, but they did it, and the design works. The 5.5 inch baffled down tubes do not spiral completely around the sleeping bag as the name implies. Rather, the tubes on the top and bottom panels are oriented at a 45 degree angle but run in opposite directions. It would seem like the construction would get complicated at the hood and foot ends of the bag, but MontBell makes it look simple: the spiral construction terminates to a sculptured hood by adding one rounded chamber, and the foot end is neatly finished as well.

I have always been impressed with MontBell’s Ballistic Airlight nylon shell fabrics and Polkatex DWR finish, but the new 12 denier shell on the Spiral Down Hugger is truly remarkable. It’s the softest sleeping bag fabric I have seen, and it sheds water like a duck’s back.

MontBell UL Spiral Down Hugger #3 Sleeping Bag Review - 2
The Spiral Down Hugger’s hood (left) covers the face very well. It draws easily via a simple braided cord and cordlock. On the inside, the bag has a thinly insulated flap that covers the zipper (right), rather than a puffy down-filled draft tube.

The Spiral Down Hugger has a YKK #5CN two-way auto locking zipper, which is used on most lightweight sleeping bags these days. This zipper has separate pulls on the outside and inside of the bag and automatically locks, so it doesn’t open by pulling the sides of the zipper or expanding the bag during the night. To insure that the zipper stays fully zipped, there is a Velcro tab at the top of the zipper, and the Velcro does not stick to the bag’s fabrics.


I tested the Down Hugger #3 on a number of summer and early fall backpacking trips, with nighttime temperatures ranging from 26 to 41 F. I slept under the stars and in various single wall shelters.

MontBell’s sizing is a bit different from other manufacturers; size Regular fits to 5 feet 10 inches and size Long fits to 6 feet 4 inches. I needed a size Long to fit my 6 feet/170 pound frame, and found the fit much to my liking. There is plenty of room inside to wear extra clothing to extend the bag’s warmth, but it didn’t feel too roomy. With the bag lying flat, I measured the bag’s relaxed shoulder girth at 61 inches and extended girth at 72 inches.

MontBell UL Spiral Down Hugger #3 Sleeping Bag Review - 3
The Spiral Down Hugger is indeed stretchy. The left photo shows me lying flat on my back with my arms at my sides; the right photo shows the bag’s expansion with my arms raised above my chest. The benefit of a stretchy bag is the bag tends to conform to my body, so I don’t have to heat up any more inside volume than necessary.

Another remarkable finding from my testing is the bag’s zipper works almost flawlessly, meaning it doesn’t snag very easily. After recently testing a couple of bags with wretched zipper snagging problems (The North Face Beeline and Mountain Hardwear Phantom 32), it’s a pleasure to sleep in the Spiral Down Hugger. (Have you ever had the problem of having an urgent need to pee in the middle of a pitch black night, and the darn zipper snags on your bag?) As shown in the previous section, MontBell uses a thinly insulated flap over the zipper, rather than a puffy insulated draft tube. Eliminating the draft tube allows the zipper to operate more smoothly, but the zipper is not as insulated as it is in other sleeping bags.

MontBell UL Spiral Down Hugger #3 Sleeping Bag Review - 4
I tested the bag’s water repellency by placing a puddle of water on the bag and checking for leakage after an hour. To my amazement no water soaked through. This was verified in my field tests, where the bag did not absorb any water when I brushed against wet tent walls.

I measured the bag’s double layer loft at 3.75 inches, which gives a single layer loft of 1.9 inches. From our table of estimated temperature ratings based on measured loft (read our Backpacking Light Position Statement on Sleeping Bag Temperature Ratings, 1.8 inches of single layer loft translates to about a 30 °F rating, so the Spiral Down Hugger #3 is on target. Please take the time to read the referenced article and note that sleeping bag warmth depends on a number of factors.

The Spiral Down Hugger #3 is not the loftiest bag around with a 30-32 F temperature rating (see comparison table below). I found its warmth to be average. In my field testing, my methodology was to wear my basic sleepwear (dry wool socks and microfleece top, bottom, and cap) inside the bag initially, then add insulated clothing later in the night if I got cold, noting the time and temperature when I got chilly. On nights when the temperature dropped down to freezing just before sunrise, I started getting chilly around 4:00 a.m. when the temperature was around 35 F. After donning my insulated clothing (or better yet putting it on the evening before), I was able to stay warm in the Spiral Down Hugger down to 26 F, and probably could have handled even colder temperatures.

MontBell UL Spiral Down Hugger #3 Sleeping Bag Review - 5
The stuff sack provided is tapered and has two drawcords to stuff the bag down to bread loaf size. It’s simply too tight. In my opinion, the two drawcord design is overkill, extra weight, and overstuffing may damage the down over time. I prefer a stuff sack that does not overstuff a down bag, although it takes up a little more room in my pack.


The following table compares the MontBell UL Spiral Down Hugger #3 with some popular 30-32 F rated ultralight mummy style down sleeping bags. All of the bags have baffled construction, and the data are manufacturer specifications for a size Regular bag.

Manufacturer Model Temperature Rating (F) Single Layer Loft (in) Weight of Down (oz) Fill Power Total Weight (oz) Cost US$
MontBell UL Spiral Down Hugger #3 30 1.9 10 800 19 229
Mountain Hardwear Phantom 32 32 2.0 10 800 22 290
Western Mountaineering SummerLite 32 2.0 10 850+ 19 315
Marmot Hydrogen 30 2.0 11 850+ 25 319
The North Face Beeline 30 2.4 10 850+ 22 279

By the numbers, the MontBell UL Spiral Down Hugger compares favorably with other bags in terms of down quality, weight, and cost. It lags a bit in loft compared to the others, but its loft does meet our minimum expectation of 1.8 inches (single layer) for a 30 F rated sleeping bag. Note that its US$229 cost is a great value compared to the other bags, and its weight matches the Western Mountaineering SummerLite bag.


I really like the Spiral Down Hugger’s soft lightweight shell fabric, fit/roominess, non-snagging zipper, hood, and light weight. It’s very easy to fall in love with this bag, and it’s a great value compared to other ultralight 30 F rated sleeping bags. However, it is not quite as warm as the Mountain Hardwear Phantom 32, and definitely not as warm as the Marmot Hydrogen, which I have also tested. I have not personally tested the Western Mountaineering SummerLite. Bag sizing and the Down Hugger’s lack of a down-filled draft tube probably contribute to the differences. That said, the bottom line for me is to wear my camp clothes (wool socks, insulated jacket and pants, fleece cap) in my sleeping bag anyway, and I typically have no problem staying warm down into the mid 20’s F, so the Spiral Down Hugger #3 will do just fine.

Specifications and Features




2009 UL Spiral Down Hugger #3


Hooded mummy with full length zipper

  What’s Included

Sleeping bag, stuff sack, cotton storage bag


800 fill-power down, 10 oz (283 g) size Regular, 11 oz (312 g) size Long


Box, 5.5 in (14 cm) baffles

  Measured Loft

3.75 in (9.5 cm) average double layer loft, manufacturer specification not available

  Claimed Temperature Rating

30 F (-1 C)

  Stuffed Size

5.3 x 10 in (13.5 x 25 cm)


Size Long tested
Measured weight: 1 lb 4.9 oz (593 g)
Manufacturer specification: 1 lb 4 oz (567 g)


Regular fits to 5 ft 10 in (1.52 m), Long fits to 6 ft 4 in (1.93 m)


Shell and lining are 12d Ballistic Airlight nylon 0.86 oz/yd2 (29 g/m2) with Polkatex DWR. Fibers are solid core.


Spiral stretch system, three-quarter-length two-way auto-locking zipper with inside and outside pulls, draft flap on inside of zipper, Velcro tab at top of zipper, sculptured hood, braided drawcord and cordlock closure on hood, tapered stuff sack with two drawcords, heat transfer logos


Regular US$229
Long US$249


"MontBell UL Spiral Down Hugger Sleeping Bag Review," by Will Rietveld. (ISSN 1537-0364)., 2009-12-08 00:05:00-07.


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MontBell UL Spiral Down Hugger Sleeping Bag Review
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Marc Clarke
(marcclarke) - F

Locale: Front Range of the Rocky Mountains
Re: pack weight? on 07/12/2010 02:04:08 MDT Print View

Montbell Ultra Light Spiral #3 Long in factory stuff sack
Ultra Light Spiral #3 Long in factory stuff sack (using the smaller of the two draw cords) and Montbell inflatable pillow in its sack.

Edited by marcclarke on 07/12/2010 02:05:56 MDT.

Marc Clarke
(marcclarke) - F

Locale: Front Range of the Rocky Mountains
Re: pack weight? on 07/12/2010 02:12:05 MDT Print View

The stuffed size is given in the review. Please RTFM. :-(

Stuffed Size
5.3 x 10 in (13.5 x 25 cm)

jimmy benson
(biggyshorty) - F
dimensions to liters on 07/12/2010 08:10:38 MDT Print View

Hi Marc,
I did RTFM but what i'm curious about is a conversion of dimensions to liters - i've always been confused about that. i am debating between getting the super stretch #3 and the UL super stretch; i guess the only difference is a few oz of weight and maybe the packing size, that's why I was asking. thanks for your help.

Marc Clarke
(marcclarke) - F

Locale: Front Range of the Rocky Mountains
Volume of a Cylinder on 07/12/2010 11:41:50 MDT Print View

Google is your friend, as always. (Who knew?)

First, you Google "volume of a cylinder" to learn what the formula for a cylinder is, where the first page I see is:

and the formula for a cylinder is
Volume = pi * radius * radius * height

Since we may have all slept through high school geometry, we'll Google "radius", and Wikipedia helpfully reminds us that the radius is one half of the diameter (and gives us pictures, even).

radius = 13.5cm / 2

And, since we are assuming we all slept through high school geometry, we'll Google "pi" to find out what the value of pi is. We find:

which tells us that pi is 3.141592

but we'll just use 3.14 to save ourselves some typing. Besides, the measurements in the review aren't all that precise. (For a calculation this crude, we could just use 3 as the value of pi and be plenty close.)

Then you plug in the numbers from the review, using
radius = 13.5cm / 2
height = 25 cm


Volume = 3.14 * 13.5cm/2 * 13.5cm/2 * 25cm

We'll use Google to do the calculation for us (no scientific calculator needed), typing in

3.14 * 13.5cm/2 * 13.5cm/2 * 25cm =

and sure enough, Google does the math, figures out that you are using cm for dimensions, and gives you the answer in liters (kinda cool, huh?). Google says:

((((3.14 * (13.5 cm)) / 2) * (13.5 cm)) / 2) * (25 cm) = 3.57665625 liters

No text books, no calculator, no nothing. Just Google all the way.

If you have had your coffee today, you could do the same calculation in inches:

3.14 * 5.3in/2 * 5.3in/2 * 10in

which Google calculates and returns as liters:

((((3.14 * (5.3 in)) / 2) * (5.3 in)) / 2) * (10 in) = 3.61345413 liters

Presto! (Again.)

Since the stuff sack is not a perfect cylinder, but has rounded ends, you can assume that the actual volume of the stuffed MB Spiral is a little less than the full 3.6 liters, probably 3.5 or 3.4 liters.

Edited by marcclarke on 07/12/2010 12:23:47 MDT.

Marc Clarke
(marcclarke) - F

Locale: Front Range of the Rocky Mountains
Re: dimensions to liters on 07/12/2010 11:45:27 MDT Print View

Now that we have had our daily lesson Google-Fu, it is left to the reader to plug in the approximate dimensions from the picture I posted of my UL Spiral #3 long earlier in this thread to calculate the approximate volume of the long version of the sleeping bag in its stuff sack. :-)

Marc Clarke
(marcclarke) - F

Locale: Front Range of the Rocky Mountains
Montbell U.L. Spiral #3 Long and Compression on 07/12/2010 11:59:22 MDT Print View

For what it is worth, I think the Montbell-supplied stuff sack is WAY TOO SMALL (as does the original reviewer). I carry my #3 Long in a 20 liter dry bag loosely fit into the bottom of my pack rather than in the tiny factory-supplied stuff sack.

Similarly, the Montbell factory-supplied cotton storage bag that came with my U.L. Spiral #3 Long is also WAY TOO SMALL, as I literally have to stuff the sleeping bag into the cotton storage bag. I'm out shopping for a MUCH larger non-Montbell cotton storage bag.

Edited by marcclarke on 07/13/2010 00:26:08 MDT.

jimmy benson
(biggyshorty) - F
lessons learn-ed on 07/12/2010 23:39:37 MDT Print View

great breakdown. thanks again. for what its worth to you, rei has great large "natural cotton" non-stuff storage sacks for sleeping bags. i've gotten 2 in past sales for $1 each...

Marc Clarke
(marcclarke) - F

Locale: Front Range of the Rocky Mountains
Re: lessons learn-ed on 07/13/2010 00:19:10 MDT Print View

I picked up an aftermarket "natural cotton" non-stuff storage bag today. Thanks for your tip. :-)

M Stein
(a.k.a.) - F

Locale: Northern California
Inferring an EN Rating for the MontBell UL SS bag from the WM Summerlite rating on 07/15/2010 17:09:22 MDT Print View

Hello, all,

I myself recently asked MontBell customer service to provide EN ratings, and in my case, they wouldn't give it out.

But by poking around the sites linked to on Western Mountaineering's "international dealers" page, I was able to turn up the super-secret EN Rating for the WM Summerlite.

The Summerlite is +6 C/+2 C/-14 C, or for us retrogrades who use the Neandertal scale...

WM Summerlite

Treating James' experience as a baseline (where the WM bag proved warmer than the MB), we might consider the MontBell bag to be a 40 F bag, rather than a 30 F.

For what it's worth....

Ultralite Hiker
(Ultralite) - F
Re: Inferring an EN Rating for the MontBell UL SS bag from the WM Summerlite rating on 11/30/2010 14:17:53 MST Print View

"The Summerlite is +6 C/+2 C/-14 C, or for us retrogrades who use the Neandertal scale...

WM Summerlite

Thanks for this info. However, based on everything I have read here on the Summerlite (which is quite a few threads) most people say the summerlite has a pretty conservative rating. Why would WM put out a 32 degree bag that has a lower limit of 36? Or are you saying these tests were done independently of WM?

Either way, most here agree the Summerlite is true to rating, or maybe even conservative. I agree that the UL Super Spiral wouldnt be quite as warm, but 40 seems too high for the bag.

Dave -
(FamilyGuy) - F

Locale: Up there
MontBell UL Spiral Down Hugger Sleeping Bag Review on 11/30/2010 14:23:31 MST Print View

"Why would WM put out a 32 degree bag that has a lower limit of 36? Or are you saying these tests were done independently of WM?"

Yes - EN testing is done by an Independent body. For all intents and purposes, this WM is a 36 degree bag.

Ultralite Hiker
(Ultralite) - F
Stand Corrected on 11/30/2010 15:31:42 MST Print View

I stand corrected then. So 40 degrees for the UL Super Spiral, I was about to puchase but that makes me hesitate.

I find the Summerlite too confining.

Jerry Getz
(jerzyshore) - F

Locale: Southeastern, PA
The BAG of my dreams on 06/01/2011 18:08:45 MDT Print View

I am a very fidgety side sleeper, and the room afforded by this bag is truly second to none. In my opinion the best thing is the way the bag sort of sucks itself down close regardless of position, minimizing open airspace between the bag and your body. For me, that is what makes all the difference.