This post may contain affiliate links.

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.

Shop Now

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.

See Also:

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.


  1. I have owned two ultra lights since 2004 and still both in perfect condition.i purchased both at the same time , one large one regular. I did this because I camp in as cold of weather as winter offers so I figured for the weight and warmth I would be covered year round but never have needed to use but one in any condition including hammock camping and have never I mean never been cold. Of anything they are so comfortable in the morning they make it hard to crawl out of bed LOL. My best purchase ever on my entire backpacking an paddling adventures. I highly recommend the purchase they are well worth the price and will open up your way of packing to the ultralight experience.

  2. Hi,
    Just want to point out that the Ultralite only has one draft tube and it is mounted to the top of the bag so that it hangs down over the zipper to prevent cold air from creeping in. Only on some winter expedition bags like the Puma and Bison there are two draft tubes with one of them being offset so that they nest together side by side to prevent cold. The Ultralite features a full down collar and a single down-filled draft tube that runs the length of the zipper hanging from the top of the bag.

Leave a Reply

Your email address will not be published. Required fields are marked *