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Reviews > Sleep Gear > Summer Bags and Liners > Montbell ULAP Thermal Sheet > Test Report by jim Sabiston

December 04, 2007



NAME: Jim Sabiston
AGE: 53
HEIGHT: 6' 3" (1.91 m)
WEIGHT: 210 lb (95.30 kg)



Photo Courtesy MontBell

Manufacturer: MontBell
Year of Manufacture: 2007
Manufacturer's Website:
MSRP: US $180
Listed Weight: 14.5 oz (411 g)
Fill Weight: 4.5 oz (128 g)

Other details from the MontBell Web site:

Temperature Rating: 50 F (10 C)
High quality 800 fill power down
15-denier Ballistic™ Airlight fiber nylon
POLKATEX™ DWR treatment
Max User Height: 5 ft. 10 in. (178 cm)
Max Dimension: 71” – 31.5” (180 cm - 80 cm)
Stuffed Size: 4.4” x 8.7” (11 cm X 22 cm)
Color: MSCT(Muscat)

Weight Sleeping Bag: 14.6 oz (414 g)
Loft: 2.5 to 3.25 in. (6 cm to 8 cm)
Length: 72 in. (183 cm)
Width at Foot: 16 in. (40 cm)
Width at Hips:21 in. (53 cm)
Width at Shoulders (widest point): 27 in. (69 cm)
Width at opening: 16 in. (40 cm)


My initial impression was "Wow! Now this is what I call light!" When I opened the cotton stuff sack it was packed in, my next reaction was "Hmmm. Interesting green." MontBell supplied a very small stuff sack, too.

I gave the Thermal Sheet a good going over checking the various features (very few) and the overall construction (very good). I was surprised to find that the U.L.A.P. Thermal Sheet uses boxed construction, as this is not mentioned on the website, at least on the specific product page. This is a labor intensive (read: expensive) but highly desirable construction technique for down products, desirable because it permits the full lofting of all the down without the loss of efficiency associated with sewn-through construction. Aside from the extremely light weight and soft, pleasant feel of the 15 denier shell, the most noticeable item is the zipper. The zipper, which is described as 'full-wrap' - meaning that the bag can be completely opened and lie flat like a blanket, is probably not unusual. Rather, the light weight and soft hand of the bag make the zipper seem stiff in comparison. There is no draft tube inside the zipper.

The Thermal Sheet is light on features, in keeping with such a light weight product. Montbell mentions only the full-wrap zipper, but there are also four hanging loops, two at each end. The top pair are smaller and made of the same nylon fabric as the bag shell, the other pair is located at the foot. These are somewhat larger and made of a grey rope-like material that resembles flattened parachute cord or a shoelace. The only other points of note are the pull cord at the head opening and a small hook and loop closure to secure the top of the zipper when closed.

The last item I checked was the hang tag attached to the zipper pull. Interestingly, it listed the bag as an Ultra Light Down Hugger. It also listed a series of features common to the Down Hugger line , but that are not present on the U. L. A. P. Thermal Sheet. The typed portion of the tag lists the bag as "U. L. Alpine Down Hugger Thermal Sheet". It seems Montbell considers the Thermal Sheet as part of the Down Hugger line, even though it lacks its primary features - elasticized stretch seams and an adjustable foot box. No matter. These would just add weight and I really do not need those bits anyway. The Thermal Sheet seems like a simple, direct solution to what I was looking for: a very light, very packable small warm weather sleeping bag.


This is where I held my breath for a few moments. The max user size listed on the MontBell website is 5 ft 10 in. (178 cm). I happen to be 6 ft 3 in. (191 cm). A problem? I noted the listed length was 71 in (180 cm), which seemed long enough to give it a try.

I need not have worried. The bag seems tailor made for me. Just enough material to fit and keep me comfortably covered without being too snug. There is even a little maneuvering room inside, but not much! The only unusual observation is that I must zip the bag closed using the hand opposite the zipper as my arms do not have the ability to bend enough otherwise.

Fitting in the little stuff sack provided is another matter. It can be done, but I do not recommend it. It took some real huffing and puffing, but I finally got the bugger in there. The result was a very small, rock hard package. I don't think compressing the bag that much can be good for it and do not intend to use the little sack again. It is just too small and too much work. This is not really a problem for me, as I never use the manufacturer's stuff sacks, which are often of mediocre quality anyway. The supplied stuff sack is no exception. Instead, I prefer to use a dedicated, waterproof stuff sack. There are many options on the market, but I used a Sea to Summit waterproof sack that I had handy (size small) that worked out quite nicely. This has the important advantage of providing an excellent weather seal for the down bag when in my pack. As I canoe or kayak nearly as much as I backpack, this is an important consideration for me.


I will be using the U. L. A. P. Thermal Sheet in a variety of applications, all oriented around lightweight backpacking. It will be used in tents, hammocks and on the ground under a tarp. The idea will be to test the light bags effectiveness in the three most popular backpacking shelter styles. The hammock and tarp applications will expose the bag to wind and weather to some degree as well.

One of my primary interests is using the bag more as a blanket than a bag by opening it using the full length zipper. I find this is actually more comfortable in warm weather with warmer, heavier sleeping bags.



1 - The lightest sleeping bag I've ever seen!
2 - Quality construction.
3 - minimal features.


1 - The color takes some getting used to.

This sleeping bag looks like it has enormous potential to be a terrific warm weather sleeping bag. Come back in about two months and we will see how things work out!



This summer is proving to be a very stable one with little in the way of extreme or unusual weather. Hot daytime temperatures typically around 88 F (31 C) and night temperatures no lower than 68 F (20 C). Occasional rain has come by, but nothing terribly heavy. In other words, ideal summer weather for the Northeast.

My six nights have been spent either on Sand Island on the Great South Bay, or camping near Grandfather Mountain in the Blue Ridge Mountains. Aside from generally higher humidity and more frequent rain in the mountains, conditions varied little from island to mountain as far as weather goes.

All nights have been spent in tents, either my solo tent (Black diamond OneShot) or a larger family tent shared with my wife.


There is no question that the Thermal Sheet is going to become a mainstay of my warm weather sleeping kit. The extremely light weight and very small back size make it the smallest, lightest sleeping bag I've ever used. I've experimented with various sleeping bag alternatives over the years, mostly sleeping bag liners of various sorts. All have been noticeably heavier and packed larger. None have been as warm.

This little sleeping bag is a small wonder and is a pleasure to sleep in. I should comment that I do not use the Thermal Sheet as a 'sleeping bag'. I have found that the Thermal Sheet works best as a quilt in warm weather. My favored method is to zip up only the lower 12 in (30 cm) or so of the foot area, making a small foot box. I leave the rest of the sleeping bag open. I sleep by putting my feet into the 'foot box' formed by the partially closed zipper and lie under the spread out bag, effectively using it sideways - zipper opened to the left and right and facing down, instead of closed and to one side. This increases the effective room enormously with little lost warmth, as all the down is to the sides and above me, not underneath where it would just be compressed.

The foot box arrangement ensures that my feet are properly covered (warm!) and the sleeping bag is positioned properly as well. A sleeping pad on the ground provides all the ground insulation I need there. The length of the bag is exactly right for me, covering right up to my chin. There is insufficient length to cover my head, but this was expected. For cooler nights, even in summer I carry a very light fleece hat, but I have had no need to use it yet. Using the Thermal Sheet like this allows far more movement and has proven to be very comfortable and effective. The upper zipper is actually unnecessary when the bag is used this way and could save a bit of weight if removed!

I found a silnylon stuff sack at an outfitter in North Carolina and replaced my waterproof stuff sack with this very nice lighter version, saving several ounces in the process. The Thermal Sheet stuffs easily into this little sack in seconds and is at no risk of getting wet once packed. The sack was very inexpensive and is a huge improvement over the stuff sack supplied by Montbell and I highly recommend doing this. It is an essential precaution when canoeing or kayaking and I consider it cheap insurance when backpacking.

I have had no issues at all with keeping comfortable, but this stable, consistent summer has not really challenged the bags rated temperature of 50 F (10 C) either. I'm a warm sleeper, too, accustomed to pushing the temperature ratings of sleeping bags well past their intended limits. I have been very comfortable with no need to wear any extra cloths or insulation at all. In fact, it has been pretty common for me to vent the bag when I overheat under it. The soft, light feel of the bag make it a dream to sleep under. It is so light that I have found myself checking to make sure my legs are under it on occasion!


The Thermal Sheet is the near perfect summer sleeping bag for my style of backpacking. The size and length of the sleeping bag are perfect for me, being just long and wide enough, with little or no excess material, keeping the weight to the bare minimum to get the job done, especially when used as a quilt.

I occasionally zip the bag up fully closed just to check the fit, which is very tight for me. I do fit with no compression of the down but there is no extra room to speak of. No surprise here, given that I am a full 5 in (12 cm) longer than the stated maximum height for the bag.

The Thermal Sheet is proving to be the ideal companion piece for a very lightweight summer backpacking kit. With my solo tent and a very small Torsolite sleeping pad, I have a full tent shelter and sleeping system weighing in at just over 3.5 lbs(1.6 kg). Not bad at all!

Negatives? I'm looking but I can't come up with any that aren't inherent in the tight fit of the sleeping bag, but this also contributes to that wonderfully light weight. In a perfect world, Montbell would offer the Thermal Sheet with either a very short zipper for the 'foot box' or construct the bag with a sewn in foot box and no zipper at all. This would make the bag even lighter and pack a bit smaller. I suspect it would still make an excellent sleeping bag liner, too.


The next couple of months will finally bring cooler weather. We are already seeing the first drops in temperature indicating that fall has indeed arrived. My priorities will be twofold. First, of course, is to seek the lower limits of comfort. Second, is to experiment with different shelter/sleeping systems.

The two systems will be a hammock and tarp combination and then just a tarp, now that the bugs will be dying off in the cooler weather.



As expected, cooler weather arrived with autumn, but the change was a very gradual one. Temperatures have been seasonal for the Northeast. starting with mild night temperatures around 60 F (16 C) and ending with night temperatures dipping as low as 35 F (2 C) in the last few weeks. Weather has otherwise been typical, with a mix of conditions due to the changing seasons, but tending towards the dry side. I have been fortunate enough to not get caught in any significant rain for the entire test period. Locations have been limited to Sand Island, Harriman State Park and my backyard as I sought out different temperature ranges as one of my primary goals at this point. Not surprisingly, the last few weeks have been too cold for the Thermal Sheet, which Montbell rates at 50 F (10 C).


I succeeded in trying out the Thermal Sheet in all my favored shelters. The sleeping bag performed well in all cases, with my experience being predictable in the that the bag could be pushed to lower temperatures in a tent than in a hammock or under a tarp, but the difference was not that great, especially if the tarp was set up properly to be an effective wind block. I have continued using the bag in my 'quilt' arrangement as described above. The only time this became an issue is in the hammock or under a tarp when the breeze managed to find its way under the edge of the open sleeping bag. The closed shelters (tent and bivy) have an advantage here in borderline conditions, as they more effectively protect from the wind.

I tried using the sleeping bag in a 'sausage' arrangement with my open hammock (with the bag wrapped around the outside of the hammock). It worked, but not very well, as the trim dimensions of the bag are just a bit too small and I felt the fabric would not hold up for long to the stresses imposed on it. Of course, the bag is not designed for this type of use either. Using it in the quilt arrangement inside the hammock made for a happy combination for warm weather. The coldest night I tried this was about 60F (16 C) and I was quite comfortable, using a light insulating layer under my back and the Thermal sheet snugged around me as a quilt.

My favorite combination is the bivy/Thermal Sheet. The sleeping bag and shelter combination come in around 2 lbs (.9 kg) and packs very small. My favorite night of the test was spent on top of an exposed ridge in Harriman State Park on a clear, breezy night. The temperature was at or slightly below 50 F (10 C). I was comfortable, but only just. With no extra layers, just a t-shirt and light nylon pants, this was the night I found the lower comfort limit of the Thermal Sheet, spot on the Montbell suggested limit of 50 F (10 C). If I happened to let the edge of the bag lift a bit and let the cool air in, I noticed it very quickly. Comfort was dependent on a tightly sealed edge, even inside the bivy!

Thermal Sheet in bivy
The Montbell Thermal Sheet tucked inside a Lightsabre Bivy

A fringe benefit to the Thermal Sheet that I had not initially considered is its use as an emergency sleeping bag. The very light weight and small stuffed size make it the ideal 'just in case' sleeping bag for dayhikes. The slight extra weight is barely noticeable, making it more likely that I will actually take it along. Combined with an emergency bivy or sheet, it is possible to have a viable, even comfortable, shelter and sleeping arrangement for less than 1 lb (.45 kg).

There is no wear and tear to speak of, but the seemingly delicate nature causes me to be very considerate in my treatment of the Thermal Sheet. The shell fabric is water resistant, but only slightly. Anything more than a couple of drops will penetrate it without too much trouble, so the drysack stuff sack is a highly recommended addition. I have been very happy with my setup.

I have not used the Thermal Sheet as a liner, as the weather was never really cold enough and my alternate bags fit into the colder temperature ranges without the additional insulation of a liner. I can see the Thermal Sheet making a very effective liner for a winter bag, however. I will likely to continue to use the bag in the quilt configuration even when using it as a liner, as it is too confining for someone of my size otherwise.


I would like to see the zipper either removed or shortened a bit to save even more weight, but this is an observation oriented towards the non-standard way I settled into using the Sleeping bag.

The Montbell Thermal Sheet is now my official warm weather sleeping bag - or quilt to be more precise. I expect it to serve as my primary warm weather sleeping bag for years to come. The only limits are its trim size and temperature rating. Both are ideal for summer use and contribute to the fact that this is an extraordinarily light and small packing sleeping bag - just what I've been looking for in an ultralight summer sleeping bag.

This report was created with the Report Writer Version 1. Copyright 2007. All rights reserved.

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