Home / Gear Reviews / Western Moutaineering UltraLite 20 Sleeping Bag Review

Western Moutaineering UltraLite 20 Sleeping Bag Review

Western Mountaineering is considered by many to manufacture the best sleeping bags in the world. The quality of their products is outstanding and it is designed with the requirements of hardcore ultralight backpackers, winter backpackers, and mountain climbers in mind.

A few weeks ago I decided to replace my REI Sub Kilo 20 which never performed up to its temperature rating. Based on the emphatic recommendations of some of my Twitter and Whiteblaze.net friends, I decided to make the extra investment and purchase the Western Mountaineering Ultralite 20, shown below. Western Mountaineering bags are priced at a premium, so “investment” is the appropriate word.

Western Mountaineering Ultralite 20 Sleeping Bag

The Ultralite 20 is a mummy style bag rated for 20 degrees and contains 850 fill goose down. The 6 ft. model weighs 28.7 oz and has 5 inches of loft. The fit of the bag is fairly snug, particularly around the shoulders, with a girth of 59″.  It also has a draft collar, which seals across your chest to prevent heat loss from the “bellows effect” when you move around at night. This is a very unusual feature on a 20 degree bag and something you usually only find on winter bags with a temperature rating of 0 degrees or lower.

Snag Proof Zipper, Western Mountaineering Sleeping Bag

One of the issues I had with my old Kilo 20 was that the zipper snagged constantly. On the Ultralite, there is a 2 inch strip of nylon on either side of the zipper that runs facing your body up the entire length of the bag and prevents the zipper from snagging. You can see a closeup of this protective barrier in the photo, above. It’s amazing: the zipper never snags. Ever.

I field tested my new Ultralite 20 this past weekend on a 3 night, 40 mile hike of the Long Trail in Vermont. The nights were a lot colder than we expected, with temperatures dipping into the mid-30’s. The Ultralite performed brilliantly. I was warm every night and far warmer than I ever was in my Kilo 20.

On the first night of my trip, I remember slipping into the Ultralite. Within 2 minutes I felt this incredible warmth envelope my entire body, which I attribute to the 900 fill goose down. I tried using the draft collar and that worked great too. In fact, I was so warm that it was unnecessary to use the mummy hood at all, and I slept all 3 nights with a light polypro hat on instead.

After this weekend, I am really looking forward to using my new Western Mountaineering bag on the rest of my Long Trail section hikes this summer and fall. If you are looking at $250 down sleeping bags for 3 season use, I strongly recommend that you consider upgrading to the more expensive Western Mountaineering Ultralite 20.

Disclosure: The author owns this product and purchased it using their own funds.

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  1. Excellent review! Here in Idaho and the Northwest spring and fall overnight lows often hit below freezing, but typically range in the low 30s to low 40s. Do you think this bag would hold up to temps between 20 and 30? I'm on the hunt for a new ultralight bag…

    Keep up the great work! You gear reviews are quite stellar. Want to swap blogroll links?

  2. I'm pretty confident that this bag will hold in those temps, but regardless of the bag you get you need to make sure you have a pad that is sufficiently thick between you and the ground, since your bodyweight is going to compress the insulation something awful. For temperatures under 30 degrees, I recommend the Downmat 7 from Exped, but it weighs more than most ultralighters can tolerate, like just under 2lbs, but you can probably extend this bag to 0 degrees with it. Another alternative is to pile on Torsolites until you get at least 2 inches of insulation underneath you. Long answer.

    Yes – definitely to trading blogroll links. I've checked out your site in the past and love it. You provide the community an invaluable service!

    Thanks for the compliments on the gear reviews. They are fun to write and I always learn something when I try to explain stuff, you know?

  3. I am still using a Western Mountaineering bag I got in 1985. They really are investment grade. It probably cost $300 in 1985 dollars, so today's prices are a relative bargain.

  4. Philip, how small does this bag compress to? Would it be possible to add a photo to the post? I will definitely consider this bag if I decide to backpack on through the Japanese fall.

  5. Jason – No problem, I'll shoot a photo tonight and post it (have to go to work now). The WM Ultralite compresses very nicely – I can get it into an 8L stuff sack if needed.

  6. Thanks Philip! I agree, it compresses nicely.

    I just bought a Sea to Summit brand compression bag for my new Big Agnes Seedhouse SL2 tent (which I've yet to use!). I like their compression bag features, and cool name to boot.

  7. I have a WM Alpenlite, which is the wider-cut model of the Ultralite. It is a fantastic bag.

    WM lists the stuffed size of their bags on the specification page. The Ultralite fits in a 7×13 sack, the Alpenlite in an 8×15 sack. It is tempting to cram it as small as possible, but I'd rather not overcrunch the down on my expensive, warm bag.

  8. Hi,

    Have you ever considered quilts? It would seem like the next step after tarps and ground clothes?

    I bought a JRB 10×11 tarp and a JRB quilt for my hammock.

    Sorting through my gear last night, I realized that, if combined that with the z-rest and the footprint from my MH Lightwedge2, I have the potential to put together real UL shelter and sleep systems.

    Might have to try that.


  9. Earlylite,

    Thanks again for your blog. I've learned so much from it. I am always looking to upgrade my gear and shave ounces. I have been using quilts for backpacking the last several years but am now probably going back to bags as I get cold easily in my quilts and they're not much lighter than certain bags. I think I am going to end up getting the Western Mountaineering Summerlite bag and I have been reading up on WM bags. I've only seen one negative comment on them. One person said he preferred Feathered Friends bags because they are more water resistant, warmer, and don't leak as much down. How do you find the shell fabric of your Ultralite bag as far as dealing with condensation, rain spray, or leaking down?

    I've also been considering getting a bivvy for tarp camping. Have you had any issues with your Ultralite when using it with your MLD bivvy? Thanks for any information you can share and happy trails.


  10. Great questions. I have mixed feelings about the shell fabric of my Ultralite bag. I wish it was a bit more water resistant, but it does dry very quickly when it gets damp. Mind you, it hasn't gotten damp since I started using the MLD superlight bivy last April, and I feel that they're a prefect combination, although I use a Montbell thermal sheet now for 40+ nights. http://sectionhiker.com/montbell-u-l-spiral-down-

  11. Earlylite,

    It sounds like you don't get condensation on your sleeping bag when using a bivvy then. I haven't used bivvies and I wondered if there would be condensation since the bivvy lies on top of the bottom half of your bag. The MLD bivvy must breathe well enough to avoid that. I also assume you get added warmth out of a bivvy, that would be a plus in some situations. Ever feel claustraphobic in bivvies? Or, does it ever get too warm on summer nights?

    The Montbell thermal sheet seems like another tempting addition to my gear collection. Seems like a good dual use item, as a warm weather bag and light enough to use as a quilt on top of another bag in cold seasons(if one doesn't want to spring for another pricey WM sleeping bag). Thanks again for all the great info.


  12. Yep, no condensation with the MLD bivy despite camping in plenty of high humidity site. No claustrophobia either. There's no real difference sleeping under it vs. a head net, which I've been using plenty the past few years under tarps when it's warm. I mainly use the bivy to prevent splashback from rain. I also like the thermal sheet – great warm weather option.

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