The Western Mountaineering UltraLite is an 850-fill down, 20°F / -6.67°C, three-season, mummy sleeping bag weighing 29 oz / 936 g. Western Mountaineering has a reputation for being conservative in their bag ratings (meaning that you can trust a 20°F / -6.67°C bag to be a 20°F / -6.67°C bag), and the UltraLite is no exception to this trend.
Western Mountaineering does not use any hydrophobic treatments on their down (which is ethically-sourced), stating on their website that they believe the “performance enhancements of hydrophobic treatments on high quality down are widely overstated.”
Testing Conditions
I used the UltraLite hiking 1,000 mi / 1,600 km on the Pacific Crest Trail and on numerous shorter trips including the Wonderland Trail and the Lowest to Highest Route. Basically, I've spent a lot of nights in it in wildly diverse conditions (rain, snow, desert, back of a car, etc.)
UltraLite Notes
- I have the 6 ft / 180 cm UltraLite – this is the version reflected in this review; it's also available in 5'6″ (165 cm) and 6'6″ (200 cm) versions.
- Yes, there are two 20°F / -6.67°C Western Mountaineering bags, the UltraLite (the one we're discussing here) and the Alpinlite. The Alpinlite is a wider sleeping bag. This means that the Alpinlite has more room, more fill, more weight, and more cost.
- All lengths of the UltraLite come in both left and right-hand zip versions but due to varying stock, you may have to search a bit to find the one you want (if the zipper side is important to you). I have a left-hand zip.
The Specs
- Temperature Rating: 20°F / -6.67°C
- EN13537 T Comfort: 25°F / -4°C
- EN13537 T Limit: 14°F / -10°C
- EN13537 T Extreme: -21°F / -29°C
- Shape: Mummy
- Weight: 29 oz / 936 g
- Fill Weight: 16 oz / 454 g
- Fill: 850-fill down
- Loft: 5.5″ / 14 cm
- Baffles: 5.25 in / 13.33 cm Spacing/Continuous
- Collar: Full/Down
- Zipper: Full length 5 YKK – left or right hand zip available
- Inside Girth – Shoulder: 59 in / 150 cm
- Inside Girth – Hip: 51 in / 130 cm
- Inside Girth – Foot: 38 in / 97 cm
- Stuff Size: 7 x 13 in / 18 x 33 cm
- Color: Blue
- Sizes: 5'6″ (165 cm), 6′ (180 cm), 6'6″ (200 cm)
- Country of origin: USA
- MSRP: $525
The Features
- ExtremeLite shell fabric encases insulation without unnecessary weight
- 16 oz / 454 g of ultra-premium, 850-fill down insulation
- Interlocking draft tubes and a down-filled collar prevent drafts
- Slightly narrower shoulder girth to eliminate pockets of dead air for improved warmth retention
- Comes with a stuff sack and a storage sack
- Warranty covers the bag against manufacturer defects for life.
- Western Mountaineering bags are made in the USA
Hood 
Foot 
Zipper
The Good
The Warmth: The Western Mountaineering UltraLite is a 20°F / -6.67°C bag. There are many standards for measuring the warmth of a sleeping bag and sometimes a bag's rating reflects its comfort limit while other times it reflects its survival limit. According to Western Mountaineering, the T Comfort rating of the UltraLite is 25°F / -4°C (the lowest temperature a female can remain comfortably warm at), the T Limit rating is 14°F / -10°C (the lowest temperature a male can remain comfortably warm at), and the T Extreme rating is -21°F / -29°C (the temperature at which you could – possibly – be kept alive by the bag without literally freezing to death). I, a male, have found this bag keeps me plenty warm on below-freezing nights approaching 20°F / -6.67°C.
The Weight: The UltraLite is truly awesome as a lightweight 20°F / -6.67°C bag. I have long been curious about experimenting with various other bags and quilts, but even most quilts with similar temperature ratings only weigh an ounce or two (< 60 g) less than the UltraLite. I've yet to find another 20°F / -6.67°C bag that can claim this weight and this warmth (other 20°F / -6.67°C bags may claim this temperature rating but might not be as conservative as Western Mountaineering in their ratings and won't actually keep you warm below freezing). At just 29 oz / 936 g with 16 oz / 454 g of down fill, the UltraLite has a fantastic warmth to weight ratio.
The Quality: With a premium price tag, you're also getting premium quality. The UltraLite has held up very well and if you take care of it, it will take care of you. I've washed it once since using it, and I've yet to find any rips, tears, or damage in the bag. Every Western Mountaineering Bag is signed by the people who stitched it together so if you ever decide to complain, you will know exactly who to blame (but let's be honest, it's probably you who is to blame).
Collar 
Top half (zipper) 
Bottom half (zipper)
The Okay
The Zipper: The Western Mountaineering UltraLite has a solid zipper. It's not the witchcraft-inspired zipper of my Montbell Down Hugger, but it's not going to snag on you every time you zip either. There's a flat, stiff piece of fabric running the length of the zipper to prevent snagging, but I still manage to get some fabric stuck in the zipper every once in a while. That said, I've never had trouble getting it out (and I've never had a tear whilst doing so).
The Bulk: Despite the UltraLite being very lightweight, it does have a small amount of bulk. I can fit it (without too much trouble) into an 8-liter stuff sack, but don't know that I would want to go any smaller (maybe a 7-liter sack, but that's probably pushing it).
The Velcro: The UltraLite has a small velcro strip at where the top of the zipper meets the hood. It's meant to completely close the down collar and prevent the bag from coming unzipped unintentionally. I've never really felt that it's been necessary and it can be a little strange closing it up all the way while inside the bag, but it's fine, I guess.
Hood + collar 
Drawstring 
Packed in 8 L stuff sack
The Bad
The Price: You want a premium, American-made product that's “guaranteed against manufacturer’s defects for an unlimited time”? Yup, it's going to be a little expensive. The UltraLite has a retail price of $525 US (the short version is $15 less and the long version is $15 more).
Velcro closure (open) 
Velcro closure (closed) 
In an 8 L stuff sack
Who is it for?
Beginner Backpackers: Honestly, the only reason I wouldn't suggest that you get an UltraLite as a beginner backpacker is the price. However, if the price is not an issue, the UltraLite is an amazing bag to consider – even as a beginner. It will serve you well for three-season backpacking (that is, anything outside of winter or deep into snowy shoulder seasons). If you take care of it, you won't have to worry about replacing it for a very long time (or maybe ever).
Weekend Warriors: The UltraLite is definitely worth considering as a weekend warrior/casual backpacker. Again, if the cost is an issue, there are some less expensive options available to you, but if you can swing a $500+ bag, then it's worth considering. It's something you won't have to worry about upgrading or replacing until you decide to start winter backpacking.
Thru-hikers: For thru-hikers, the UltraLite is the gold standard of sleeping bags. You could go with the 10°F / -12°C Versalite if you want something warmer, but as far as 20°F / -6.67°C sleeping bags go, you can't do much better than the UltraLite (unless you want something wider – then check out the Alpinlite).
Most-popular Alternatives
| SLEEPING BAG | PRICE | WEIGHT | TEMPERATURE | FILL | FILL WEIGHT |
|---|---|---|---|---|---|
| Western Mountaineering Versalite | $605 | 32 oz / 907 g | 10°F / -12°C | 850-fill goose down | 20 oz / 565 g |
| Western Mountaineering Alpinlite | $585 | 31 oz / 879 g | 20°F / -6.67°C | 850-fill goose down | 19 oz / 539 g |
| Feathered Friends Swallow UL 20 | 27oz / 766g | 20°F / -6.67°C | 950+ goose down | 16.7 oz / 476 g | |
| Enlightened Equipment Revelation 10 | $325 | 25.95 oz / 736 g | 10°F / -12°C | 850-fill duck down | 13.63 oz / 386 g |
| REI Co-op Magma 15 | $370 | 28.2 oz / 800 g | 16°F / -8.9°C | 850-fill goose down | 15.9 oz / 451 g |
Conclusion
The Western Mountaineering UltraLite is my go-to sleeping bag for three-season trips into the mountains (the keyword here being “sleeping bag” – we're not talking about quilts here).
If you have the budget and you aren't an especially cold sleeper (and you aren't going to be making trips deep in a shoulder season), then I would definitely recommend the UltraLite. But again, if you want something warmer, check out the Versalite instead (slightly heavier and bulkier, but a 10°F / -12°C bag instead of a 20°F / -6.67°C bag).
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My WM UltraLite is now over 20 years old, and has over 7,000 trail miles. It continues to serve me well, and has a great balance of warmth and weight. It has done multiple AT & PCT thruhikes. I have used it comfortably down to 0 degrees with a lightweight bivy while sleeping in mid-weight long johns.
About 3 years ago, I had a local shop add ~3 ounces of 850 down to re-energize the warmth. (Or maybe it is my slowing 50+ metabolism…) The only ‘repair’ was replacing the worn velcro used at the top of the zipper.
The fabric used in this bag is very breathable which will decrease the comfort range when cowboy camping in windy areas. I would like to try a Pertex shelled version, which might allow for either less down or lower temperature range. That said, the breathable fabric allows for quick drying in the sun, and I didn’t have much of a problem with moisture accumulation on the AT. (I carried a lighter weight summer bag/blanket through the hot months.)
I have the short version, and I am 5’5″ at about 140 lbs in thruhiker shape. I am a side sleeper. My bag weighs in at ~850gr / 30 oz (including the added down).
While WM has likely made subtle design changes over 20 years, the bag on display at my local shop looks to be an identical twin of my trusted companion for 20 years.
I definitely would recommend this bag if you are comfortable in a slender cut bag and understand its limitations.
As far as the width of the bag goes, I think it now falls more in the “medium” category as there are certainly more slender bags out there. That said, the Alpinlite is a wider version of the Ultralite for anyone looking for a bit more wiggle room.
I thought it was interesting that you didn’t consider Feathered Friends to be an alternative. I’m curious why?
No reason it shouldn’t be on there – added!
Regarding other bags not being much less weight, my Kabatic Flex 15 quilt (that being the key difference, I think) weighs 25.2 ounces total in the Regular 6′ size. That includes 16.9 ounces of 900 fp down, and it costs substantially less ($410 in that version). I haven’t taken it down to 20F, but Kabatic is reputedly conservative in their temperature ratings as well. So that’s a slightly/negligibly warmer bag with 4 ounces less weight at less cost I could see how a quilt isn’t for everyone, but I particularly like how the Flex unzips to lie completely flat, which makes it useful in much warmer temperatures as well.
That’s the quilt I’m most interested in trying out at the moment. I will probably make the plunge someday soon, but I’m not ready to spend the money just yet.