Earlier this year, I bought a Montbell UL. Spiral Down Hugger Thermal Sheet (down sleeping bag) and I’m really pleased with its versatility for summer and autumn camping.
Rated at 50 degrees (F), I’ve used the Montbell comfortably to 40 degrees with down booties and long underwear (which I always wear when I sleep). Contrary to its name, it’s not a sheet and it doesn’t use the spiral system that Montbell’s heavier down bags use. It’s just a down-filled rectangular sleeping bag, without a hood, that scrunches up incredibly small in a stuff sack.
I originally bought the Montbell to use during the summer when my Western Mountaineering Ultralite 20 is simply too hot. I’ve owned other warmer weather bags in the past and not been wowed by them, but what attracted me to this particular sleeping bag was its 800 fill down, the fact that it could be used as a quilt as well as a sleeping bag, and of course the fact that it weighs 13.6 oz, well under 1lb.
So far, I’ve just used the Thermal Sheet in its sleeping bag configuration, but it does have a wrap-around zipper so that you can open it up and use it as a quilt, for one person, or even two good friends. In quilt-mode, I’d keep the bottom zipped up to my calves to create a foot box like you find on other quilts, like the Golite Ultralite Quilt.
In addition to the YKK zipper, there are two loops sewn into the bottom hem of the bag and two plastic hooks attached to the top hem. I presume these are for attaching to a portaledge, but they’re certainly not strong enough to substitute for a proper harness. There’s also a drawstring and cord lock at the top of the bag, for cinching it around the tops of your shoulders to better retain warmth.
I’ve read about older versions of this bag that did not have baffles and allowed you to move the down fill around. That’s not the case with this latest model. The baffles are sewn diagonally across the bag to keep the 800 fill goose down evenly distributed.
A Winter Sleeping Bag Liner
In addition to using the Montbell Thermal Sheet in the summer, I plan on testing it as a liner inside my 20 degree Western Mountaineering bag to boost its warmth and fill a hole in my down sleeping bag lineup, which is the absence of a 0 degree bag. This worked well without compressing the loft on the Western Mountaineering bag when I tried it at home, and as you read this post, I’ll be testing it out in the White Mountains on a late autumn overnight trip (oops, I came down with a bad cold and the trip got postponed.)
The irony of this setup is that I’ll be using a Western Mountaineering sleeping bag with a Montbell thermal sheet liner, something I can’t see either manufacturer endorsing due to their marketplace rivalry.
If it works, which I expect, then I can use the two bags together and get a functional 42.6 oz, 0-degree down sleep system, without spending the money for yet another sleeping bag. When you consider that a 0 degree Western Mountaineering Kodiak weighs 44 oz, it becomes apparent just what a good deal this really is: I’ll get the equivalent of three sleeping bags for the price of two.
Of course, it has to work, but regardless, the Montbell Down Hugger Thermal Sheet has been a resounding success as a summer-weight sleeping bag for me.SectionHiker is reader-supported. We only make money if you purchase a product through our affiliate links. Help us continue to test and write unsponsored and independent gear reviews, beginner FAQs, and free hiking guides.