Western Mountaineering Ultralite Sleeping Bag Review

Western Mountaineering Ultralight Sleeping Bag - Key Features

The Western Mountaineering Ultralite is a 20 degree sleeping bag that weighs 29 ounces. It’s filled with 16 ounces of 850+ fill power goose down and loaded with features that make it comfortable to use, especially during early spring and late autumn when there’s a touch of winter chill in the air. I’ve owned one for going on 10 years and still consider it a first-rate component of an ultralight sleep system despite the increased popularity of lighter weight backpacking quilts. While the color on the outside fabric of my Ultralite has faded a bit with age, it’s still as warm as ever.

Western Mountaineering Ultralite 20 Sleeping Bag


Premium Sleeping Bag

The Western Mountaineering Ultralite 20 Sleeping bag is a premium mummy sleeping bag with 850+ fill power goose down, a draft collar, down draft tubes, zipper tape guard, and continuous baffles. Hand-sewn in California, it's a top of the line ultralight sleeping bag for three-season conditions.

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Specs at a Glance:

  • Weight: 29 oz
  • Down Fill: 16 oz
  • Insulation: 850+ fill power goose down
  • Fabric: 12 denier nylon ripstop
  • Loft: 5″
  • Shoulder/hip/foot girth: 59″/51″/38″
  • Length: 5’6″, 6’0″, 6’6″ (6′ 0″ reviewed)
  • Zipper: full length; right or left-hand
  • Compressed size: 6-7 liters
  • EN Temperature Ratings:
    • Comfort: 24.8F / -4C
    • Lower Limit: 14F / -10C
    • Extreme: -20F /-29C

When I purchased the WM Ultralite, it was an investment. I can’t remember exactly what I paid for it, but it was one of the most expensive 20 degree sleeping bags available at the time. That hasn’t changed and Western Mountaineering bags are still priced at a premium. In fact, Western Mountaineering refuses to let retailers discount their bags, which is why they’re never on sale at a discount. What has changed is the breadth of the Western Mountaineering product line and the new sleeping bags, quilts, and hammock under-quilts they’ve started to introduce in recent years. A few years ago, it seemed like the brand was languishing. But they’ve introduced a wave of new products in the past few years and are clearly innovating with the times.

The Ultralite isn’t the only great sleeping bag that Western Mountaineering makes, but it has all of the standard features you find across the product line and that set Western Mountaineering bags apart from others:

  • Down-filled draft collar
  • Down-filled draft tubes along zipper
  • Zipper guard
  • Continuous baffles

Draft Collar

A draft collar is a tube of goose down that drapes across your upper chest and back to seal in the warm air inside the sleeping bag. It prevents what’s called the “bellows effect”, which causes warm air to be being pushed out the top of a sleeping bag or quilt when you move around at night. Draft collars are more commonly found on sub-zero -20 and -40 degree sleeping bags, but are just as effective in warmer temperature sleeping bags like the Ultralite 20.

Draft Tubes

The Ultralite has two down-filled tubes that run the length of the side zipper. When you zip up the sleeping bag, they come together and block any cold drafts that might make their way past the zipper.

Zipper Guard

There’s a wide piece of fabric tape that runs along one side of the zipper on the Ultralite which prevents the zipper from getting stuck in the shell fabric of the other side. I’ve ripped the shell fabric of many sleeping bags made by other manufacturers that don’t have this feature, which is a real lifesaver in preserving the exterior shell.

Continuous Baffles

The 850+ fill power goose down in the Ultralite is distributed in continuous horizontal baffles from zipper to zipper, so you can shift the down insulation from one side of the bag to the other. For instance, during hot summer nights, you can shift the down from the top of the bag to the bottom so there is less insulation on top of you. When the weather is cold, you can move the down to the top of the bag. This is a desirable feature in a 3 season, 20 degree bag because it means you can use it across a wider range of temperatures and conveys quilt-like flexibility, in terms of temperature regulation, for a sleeping bag.  It requires a bit more thought to use, but the extra flexibility is quite useful and can cut down on the number of sleeping bags you need to purchase if you backpack and camp year-round.

Airing Out the Ultralight in Scotland
Airing Out the Ultralight in Scotland


I’ve used the Ultralite 20 year-round from early spring to late autumn up and down the US East Coast and in Scotland in temperatures ranging from 15 degrees up to 80 fahrenheit. It’s fantastic for cool weather backpacking in early spring and late autumn when the days are short and nighttime temperature run between 20 and 50 degrees. I like to section hike the Appalachian Trail during “shoulder seasons” in those temperatures  and the Ultralite is perfect for that time of year. I’ve also backpacked across Scotland twice in May with the Ultralite in similar conditions.

But for temperatures over 60 degrees, the Ultralite is overkill and you have to unzip it or use it like a quilt when it gets hot out. When I first bought it, I was just getting back into backpacking and didn’t have much gear, so I used it year-round. These days I use a quilt or a hoodless sleeping bag when nighttime temps get above 50 degrees, depending on whether I’m sleeping in a hammock or on the ground.

Fit-wise, the Ultralite is a bit narrow at the shoulders and over the chest. That’s by design, to save fabric weight and reduce the amount of air that your body needs to heat up at night. Western Mountaineering sells similar bags with a wider shoulder girth if you prefer more space. As a side sleeper, I’ve never found these dimensions to be terribly constricting. In addition, the hood on the Ultralite is fairly “flat” as opposed to fitted, which makes it easier for side sleepers to use.

Western Mountaineering Ultralite in an Appalachian Trail Lean-to 2011
Western Mountaineering Ultralite in an Appalachian Trail Lean-to


The Western Mountaineering Ultralite 20 Sleeping bag is a premium mummy sleeping bag best used for nighttime temperatures under 60 degrees. It’s loaded with high-end features that you won’t find on most three-season sleeping bags, like 850+ fill power goose down, a draft collar, down draft tubes, zipper tape guard, and continuous baffles. These features cost more because they have to be hand-sewn and require more labor to make, but they really increase the performance characteristics of the bags that have them. While Western Mountaineering sleeping bags are expensive, they do retain their value over time. I’ve had my Ultralite 20 for 10 years now and it’s still as warm and functional as ever despite hard use.

If the Ultralite feels like an attractive option, you need to ask yourself whether its temperature range matches your needs. Mummy sleeping bags aren’t for everyone and with the increased availability of quilts and hoodless sleeping bags, backpackers have a lot of options available when it comes to sleep insulation. While I do prefer a quilt and hammock in warmer weather and it’s must-have in a hammock, I still like to use a mummy bag when temperatures drop below 40-50 degrees at night for the extra head and shoulder insulation they provide. My advice is to figure out what temperature range you need to cover and what you’re willing to spend before you invest in a Western Mountaineering bag like the Ultralite 20. They’re fantastic ultralight sleeping bags, but it’s best to make an educated purchase rather than an impulse buy with such a premium product.

Disclosure: The author purchased this product with their own funds.

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  1. The Alpinlite is the wide version of the UltraLite. I have the Alpinlite and love it.

    The wide/narrow option is interesting. Comparing to the Marmot Helium, with a shoulder girth of 61″ (regular length), the UltraLite is 59″ and the Alpinlite is 64″. The Helium is a good middle-of-the-road high end bag for comparisons.

    And yes, Western Mountaineering uses capitalization differently for UltraLite and Alpinlite.


  2. Come on, Phil; traditional down mummy bags are old hat! A quality down quilt, like the Katabatic Gear Palisade, will shave over 10 ounces off your pack weight vs the WM Ultralight and you won’t be sleeping in, what feels like, a straight jacket. Quilts do take some getting used to, but you need to get with the times, man!

    • Dude. I have plenty of quilts, even cold weather ones. I explained my logic regarding temperature selection between sleeping bags and quilts. Lots of thru-hikers contact me asking what sleeping bag to buy because they’re freezing their ass off under 30 degrees with a quilt. They’re easy to use in warm weather (on the ground) but there are still diminishing returns when you get below freezing. But be my guest, use one if you want. HYOH.

      • Now I’ll grant you that the Pallisade is one quilt that you might use successfully in colder weather because they stuff the thing full of goose down. But compare that with other popular quilts that are less insulating and people are having cold experiences with. I think there’s a big problem with the temperature ratings that some quilt makers assign to their quilts, when they’re driven to advertise them as lighweight as possible. It’s just like the old days when sleeping bags weren’t tested with a standard test. Call me old fashioned, but I trust the new sleeping bag temperature rating standards a whole lot more than I do some quilt manufacturers.

      • I got you there, hey!

        Look, I’ve prefaced my remarks that quilts take some getting used to. As a hammock camper, I was forced into the discipline of sleeping on my back and not moving around excessively. I have been able to transfer that to the ground, and now find I sleep just as warm, and more comfortably, than if I was entombed in a sleeping bag. I no longer even bother using a pad attachment system. The problem that I think allot of people have is that they try a quilt for a night or two, find they can’t maintain a heat envelope, and give up in frustration. Gut it out and develop a system and you’ll be rewarded in the process.

      • FYI. Apples to apples comparison. The WM Summerlite 32 only weighs 0.8 ounces more than the KB Pallisade which is a 30 degree Quilt. Hardly any difference. The WM ultralite is a 20 degree bag and heavier because it’s rated lower. In fact, it’s comfort rating is 14 degrees.

    • Or, you could have respect for the experience of others, who have been there, done that, and found it didn’t work for THEM. My experiences are much like Philip’s.

      It’s attitudes like these that led me to quit BPL after a decade.

      • Oh, lighten up! it’s not like I insulted his manhood or anything; Yeeesh!

        I thought it would be interesting to start a discussion on the merits of sleeping bags vs quilts, that’s all. Regarding Phil’s comments above, the Summerlite is a (mostly) warm weather bag with a 59 inch shoulder girth. Did you ever try to sleep in something this narrow? While the Palisade is rated at 30 degrees, it is really a 25 degree bag, with baffles of 2.25″, versus 2.0″ on the Summerlite. Also, the wide version of the Palisade equates to, roughly, a 67″ shoulder girth on a traditional mummy, allowing you to comfortably wear a down puff jacket in the bag. This all adds up to a solid, three season sleep system that is a valid alternative to the Ultralite.

      • Rex is a good guy. Give him a break.

  3. I have been using an Ultralite and Summerlite for many years and they both work well for me and the temperature ratings are right for me. I do a couple of winter trips each year where the temps get down in the single digits over night (maybe 5 deg F). I have been using my Ulttralite with a liner and some additional clothing but I would like a bag rated for single digit temps. I am considering a WM Antelope MF. I would appreciate your input Philip. Thanks!

    • Looks like a bomber bag!

    • I’ve nested the WM UltraLite + HighLite to handle temps a bit colder than I find comfortable in the UltraLite. A few ounces more and a bit bulkier to carry than purchasing a bag that could handle the lower temps – but a good compromise.

  4. Yes, I agree with Philip. The ultralight is a GOOD bag. As far as a quilt goes, I believe that you miss the extra insulation needed under you at lower temps, ie <20-25F. They simply allow to much air in through drafts.

    Unless you have a high performance DAM (Down filled Air Mattress,) or, under quilt for a hammock, quilts in general suffer at lower temps. Saying a 20oz/20F EE Revelation is the same as a 29oz/20F WM Ultralight looks like a big PLUS for the Revelation. But sleeping on the ground or in a hammock with no pad at 40F will show this to be unfounded. You will be cold at 40F under the Revelation and still warm in the Ultralight. So a pad is needed with either to be comfortable at their rating. (While loft is lost below you when sleeping on down, it is apparent that down still insulates at a reduced rate over nothing.)

    To evaluate the two, it becomes apparent to me that an under pad/under quilt is necessary to properly "compare apples to apples" at the rated temps. Disregarding overall comfort, a Neoair at 12-13oz will be needed under the quilt. A 7oz 1/2" CCF pad is all that is needed under the Ultralight. Since a 1.5oz Hoodlum is also necessary to meet the 20F rating of the Revelation, the actual weight of the quilt system is 34-1/2oz. The actual weight of the bag system is 36oz. Of course, the 1.5oz difference does NOT include the drafts (which as a restless sleeper, I find annoying with the Revelation.)

    Basically, when we start talking about temps less than 32F/0C, we are NOT talking UL gear. Rather, we are talking light weight gear. While it is OK to occasionally extend a UL kit to 20F by wearing all your clothing to bed, you should not plan on that temp overall. In general, a <10# UL kit is good to 32F with some margin for survivability. But, it is not a good kit when you expect less than 20F. For UL kits ounces count. For this and the reason above, I discount the 1.5oz difference.

    Generally, I find that these rules work pretty well for experienced backpackers and have some reserve survivability depending on the exact weather conditions:
    For XSUL, 50F, nearest gram counts.
    For SUL, 40F, nearest 5 gram counts.
    For UL kits, 30F, nearest ounce counts.
    For LW kits (LightWeight) kits, 10F, nearest 8oz count.
    For Normal Backpacking kits, -10F, nearest pound counts.
    For HW (Heavy Weight) kits, >40# base, >-40F, nearest KG(2.2#) counts.

  5. I absolutely love my WM Megalight for all the reasons Philip mentions about the Ultralight. I thought I would never buy another bag. But when I found myself using it unzipped as a quilt about 70% of the time I made the move to quilts (EE) and I think the move is permanent. I say this not to argue the merits of bags vs quilts, nor to convince anyone that their decision is incorrect, it is simply *my* decision. Even with a 64″ shoulder girth I find the Megalight more restrictive that I like. As Philip said, HYOH.

    That said I still own, and cherish, the Megalight and would not hesitate to use it again should the conditions dictate. With all the down shifted to the top (which is the configuration in which I would use it) I have slept happily down to the lower teens. Not bad for a bag rated to 30 deg.

    Lastly, I consider a high quality bag to be a required element of a complete sleeping system quiver. It’s all about choices and matching the gear to the conditions. No one element is appropriate for all conditions.

  6. I have an Alpinlite which I like very much if the conditions are right. At 6 foot / 185 lbs. the ultralight is too narrow and gets twisted around me. I toss n turn a lot. The hood is great for keeping the pillow in place. The coldest I ever used it was a dry calm 22 degree desert night wearing shorts and a fleece shirt. Slept like a rock. But like you say Phil, I will not use it over 45 degrees. Even in quilt mode it’s too hot. And long mummy bags make lousy quilts with my feet burning up in the foot box and the hood flopping in my face.
    Recently I bought an EE Convert, 10 degree. It’s 6 ounces lighter and just as warm. It can be used in blanket/quilt/bag modes. Of course I have to wear a parka or hat to bed when cold, and the pillow can get away from me but I have to admit, I do like it better.
    In my opinion, quilts are for summer, semi-rec bags are for shoulder season, and mummy bags are for extreme cold. That’s my 2 cents.

  7. I have a semi-rec bag but it’s only good down to about 25-30. I have had a hard time finding a colder bag. An ex of mine had a 20 degree Sierra Designs down bag that I loved but they don’t make it anymore. Any ideas on a10-20 degree down semi rectangular bag with a full zip? If they could zip together even better.

  8. Let’s see it was about 1999 when I bought my Ultra lite. I needed to replace my old bags (Cats Meow & Blue Kazoo.) for any future Sierra Trips and wanted something Warm, and Light Weight and especially since I now had the money to buy whatever I wanted…Which always helps… Having spent a week with someone in the Sierra’s who had one, and who I traded for one night at 11,448 feet I was sold. The Bag is perfect for those dry Cold Sierra Nights and those sudden temperature drops as the Sun goes down… As soon as I arrived home I sent away for it… Upon arrival I could not find one flaw in the stitching nor the materail, it was a perfect bag…. I have a saying that I use when I buy a House and a Car or anything over $100.00… “If my money has to be perfect, then whatever I am buying has to be perfect”… The bag to this day is in like new condition… Being I hike in the damp south most of the time I still used the Meow and Kazoo most of the time but for cold Winter.. it is the Ultra Lite…..

  9. OK. I use a 20F EE Revelation (20 oz,+ 2oz. Hoodlum), -10F EE Convert (33 oz. + 4oz. Hoodlum), WM Ultralite 20 (29oz.), and -40F custom made mummy (5 lbs.).

    Slept last night in a Hilleberg Niak using Revelation with Hoodlum.. Temp 25F. Woke up several times due to cold draft due to me shifting under the quilt. I would have been comfy in the Ultralite.

    In my experience the quilts are great down to 32F. My hoodless mummy (EE Convert) to 0F. Mummy to what the EN rating is. Each is a tool and many people use the wrong tool for the job. A crescent wrench approach to outdoor life is haphazard at best and dangerous at worst. I like each quilt/bag for its intended purpose.

    Last night I slept beyond the edge of the Revelation. Really hoped for comfort at 25F but will continue using the Ultralite below 32F. I really like the Ultralight because of its extended range of comfort. I usually carry it when overnighting in shoulder season whilst snowshoeing or skiing. Got caught in 19″ surprise snow storm a couple of weeks ago and the Ultralite made the unplanned extra day/ night warm and safe.

    To each his own, but gotta love the Ultralite. If I were limited to use only one sleep system it would be the WM Ultralite.

  10. Philip,

    I bought the WM Ultralite 20 last year and I’m just getting around to buying a compression sack for it.
    Can I get away with a size small? (7 x 16 before compression) or should I size up to medium?
    I want to go ultra light on the compression sack. Do you recommend a particular compression sack?

  11. I find the continuous baffles are a negative, for the same reason you think they are a positive. The down will move easily when and where you don’t want it to. I think it is just clever marketing from the manufactures to turn a negative into a positive.

  12. Another very useful discussion/debate! I’m always looking for ways to cut weight in the “big 3” without sacrificing safety or too much comfort loss. Hey, age takes it toll…

    I bought the WM Versalite over 10 years ago. Best purchase I’ve ever made. Most of my big trips are solo in the Wind Rivers in mid-to-late September. Lows at near 10K can easily be 10-35F. I tend to sleep a little warm, but want to certain I am (1) safe and (2) comfortable. For 2 lbs, the WM Versalite does that.

    I checked with a local outfitting store. They sell/rent 0F bags almost entirely. But, they said when WM states it’s good to 10F, they mean it.

    Those that camp in milder conditions, or are willing to take a chance with a possible 10F night, maybe a 20z 30F quilt would be fine. My only complaint with the Versalite is that it’s occasionally too warm, especially at the beginning of the night. More than happy with that tradeoff.

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