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Hands-on Gear Review

Western Mountaineering Ultralite 20 Review

Editors' Choice Award

Backpacking Sleeping Bag

  • Currently 5.0/5
Overall avg rating 5.0 of 5 based on 1 review. Most recent review: November 22, 2015
Price:   $470 List | $470 online
Compare prices at 3 resellers
Pros:  Excellent loft, no catch zipper, warm, lightweight
Cons:  Very warm for mid-summer, weak velcro closure for draft collar
Manufacturer:   Western Mountaineering
Review by: Mike Phillips ⋅ Review Editor, OutdoorGearLab ⋅ November 22, 2015  
The Western Mountaineering Ultralite is an excellent 3-season backpacking sleeping bag. It is best suited for mid to high elevations during mid-summer, and is warm enough to take along on late spring or early fall trips in the mountains. Its wider sibling, the Western Mountaineering AlpinLite, previously won our Editors' Choice award for its overall quality and reliable performance. However, it has been usurped. Those with narrower shoulders and the weight/space conscious backpacker will find the UltraLite to be a better all around sleeping bag. If you're a bigger person or plan on wearing a down jacket to bed, consider the AlpinLite. We don't mind the slimmer cut of the UltraLite and consider this bag to be the best all around, 3-season, backpacking sleeping bag in this review.

As with other Western Mountaineering bags, we like that it is made in the U.S.A., uses ethically harvested down and has simple, functional features.

RELATED: Our complete review of backpacking sleeping bags

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OutdoorGearLab Editors' Hands-on Review

While not ultralight when compared to some of the minimalist traditional backpacking sleeping bags in this review, or those for the uber weight conscious user tested in our Ultralight Sleeping Bag Review, the Western Mountaineering UltraLite is one of the lightest bags in our Backpacking Sleeping Bag Review. The Western Mountaineering Alpinlite is a slightly wider version of the UltraLite and is a good fit for bigger people and those that prefer a wider bag for comfort's sake, or to layer more clothes in cold weather.

Performance Comparison

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Color coded sizing. The Western Mountaineering AlpinLite (red) is slightly wider than the UltraLite(blue).
Credit: Mike Phillips


While we appreciate the extra space to roll around or throw a jacket on in the AlpinLite, the UltraLite is a much more thermally efficient sleeping bag for average sized users. Remember that fit is a crucial component of a warm sleeping bag. The more dead air space inside the bag, the better chance for cold spots and disrupted sleep. The 20 degree Fahrenheit rating of the UltraLite is conservative. Near the bag's limit it was comfortable with the draft collar and hood cinched properly.

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Very inviting lofty down and soft, lightweight fabrics on the Western Mountaineering UltraLite.
Credit: Mike Phillips

Similar to the AlpinLite, the UltraLite features continuous horizontal baffles. This design allows you to shift down from the top of the bag to the bottom of the bag or vice versa. This is a very functional way to control the temperature inside your bag. You can have more insulation on the top of the bag for cold nights and the opportunity to shift that down to the bottom where it can be compressed and be less useful for keeping you warm on those hotter nights.


The UltraLite weighs 29 ounces in the 6'0" option. It is the fourth lightest bag in this review, but one of the warmest. The slightly wider AlpinLite is 3 ounces heavier.

The UltraLite uses Extremelite fabric on the top and bottom of the sleeping bag. Western Mountaineering uses this Extremelite fabric on high-end sleeping bags, and it weighs less than 1 oz. per square yard. The ultra-fine yarns that make up this fabric are very soft and are ultra-compressible. Albeit a little bit fragile, it contributes greatly to the bag's low weight and high compressibility. Previously the UltraLite did not use this fabric on the entire bag. Although the weight change and compressibility difference is negligible, it made a perceived difference to us in handling the bag knowing that the highest quality materials were used throughout.

Another contributing factor to the low weight of the UltraLite is its slim cut. This is indeed one of the narrowest sleeping bags in our test. Less material obviously shaves a few grams from the overall weight.

One way to make this bag lighter would be to use a shorter zipper such as that found on the UltraLite's ultralight sibling, the Western Mountaineering HighLite.


High loft and soft, lightweight materials make the UltraLite a very inviting place to lay your head for the night. However, the narrower shoulder and hip girth of the UltraLite make it less comfortable than the AlpinLite. Similar features shared by the two, including the hood design and great draft collar, score extra points.

Let's revisit weight briefly, and its effect on comfort. Small, lightweight bags like the UltraLite are more enjoyable to carry than bulkier, heavy bags like the Sierra Designs Backcountry Bed 800, which is notably comfortable. The difference is that the Backcountry Bed is a dream to sleep in on warmer nights, while the UltraLite can more confidently handle a wider temperature range; and the UltraLite is smaller and lighter, which makes for a more comfortable bag to carry in your pack. Basically, the Backcountry Bed is awesome for sleeping, while the UltraLite is better for actually traveling.

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The Western Mountaineering UltraLite out for an early season trip in the High Sierra.
Credit: Mike Phillips

Packed Size

5 inches of loft looks like a lot to pack away when this bag is laid out on your sleeping pad. 850+ fill down and superlight materials make the UltraLite a much smaller package than you would expect when stuffed into the right compression sack. For a much more tiny package, the Western Mountaineering HighLite and Sea to Summit Spark Sp II are the most compressible bags in our review.


The continuous horizontal baffles on the UltraLite make for an easy to use thermostat. The down chambers encircle the sleeping bag from zipper to zipper allowing the user to shift down toward the top of the bag for cold nights and shift the material beneath the bag for warm nights. By opening the bag and laying it flat, you can press down and run your hands in the desired direction, pushing insulation to where you need it more or less.

Similar to the AlpinLite, the UltraLite features a reverse differential hood, which is very comfortable. This refers to the fabric on the inside of the sleeping bag being larger than the shell fabric. These hoods cover your head comfortably without needing to tighten it too much. This design was not used on the HighLite, the other Western Mountaineering sleeping bag in our review. Hoods like that one simply tighten around your face, leaving a tight circle with drawcords pressing against your face.

The one inch stiffening tape that Western Mountaineering uses on both sides of the zippers aids in easy, snag free operation.

The draft tube along the zipper and the draft collar on the UltraLite are lofty and mate well to keep warm air in, and cold air out. However, Western Mountaineering should consider a different method for closing the draft collar and the hood of this sleeping bag. Both closures are small pieces of velcro that are hard to spot and operate, and come open very easily in the night. Particularly on the draft collar, this allows some cold air to enter the bag.

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The UltraLite uses a small weak velcro closure for the draft collar and the hood of the bag.
Credit: Mike Phillips


We expect high end backpacking sleeping bags to be versatile. For most people, a single bag that can handle three season use should be the goal. The Western Mountaineering UltraLite and AlpinLite are good examples of that. For the weight conscious backpacker, a two pound sleeping bag is reasonable to carry and they are certainly warm enough for the cold nights of the shoulder seasons.

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We stayed cozy in the Western Mountaineering UltraLite even during a cold late season rain storm. Seen here paired with a NeoAir sleeping pad.
Credit: Mike Phillips

Best Application

The UltraLite is the best sleeping bag in our review for 3 season use. It is best suited for travel in the middle and high elevations mid-summer, and is warm enough to stretch your season into the shorter days of fall and transitional periods in the spring. While not "ultra-light" by comparison to bags and quilts in our Ultralight Sleeping Bag Review, it fits nicely into a lightweight backpacking kit for those who are willing to sacrifice weight elsewhere (shelter, clothing, food etc.) in order to have a warmer, more restful night's sleep.


One of the reasons that we prefer high quality down sleeping bags is that they have a long lifespan if they are well taken care of. They can be stuffed and unstuffed over and over without breaking down the insulation. Some can even be refilled by the manufacturer to restore the insulation or add more loft! If you are able to buy a quality bag that can handle most, if not all, of your on-trail (or off-trail) adventures, you will save some cash in the long run.

At $500+ for a Western Mountaineering sleeping bag you are looking at a big investment. But, if that bag can sustain 10+ years of use, and be your go-to for most of your backpacking trips, we think that it is a good investment.


The real line between the Western Mountaineering UltraLite and the AlpinLite is in the fit, and therefore a few extra ounces. For most average sized people, the UltraLite is the best choice for a 3 season backpacking sleeping bag. The UltraLite takes home the Editors' Choice award for backpacking sleeping bag because it balances easy to quantify aspects such as weight, packed size, and versatility with more subjective but practical aspects such as warmth, comfort, and versatility.

Other Versions

When ordered from Western Mountaineering directly, all of their bags can be overfilled in the foot-box and elsewhere.

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Western Mountaineering Summerlite
  • Excellent summer-weight sleeping bag
  • Very lightweight: 1 lbs 3oz
  • 850 Fill down
  • $395

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Western Mountaineering Alpinlite
  • 2 lbs (2 oz more than the Ultralite)
  • Lofty and very comfortable
  • 64" shoulder girth (5" wider than the Ultralite)
  • 850 Fill down
  • $525

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Western Mountaineering Antelope MF
  • High Performance, 5*F bag
  • 2 lbs 7 oz
  • $575

Mike Phillips

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OutdoorGearLab Member Reviews

Most recent review: November 22, 2015
Summary of All Ratings

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