The US-made WM Ultralite was the warmest sleeping bag in our review. It was also one of the most compressible and boasts a light weight and cozy internal fabric.
The 20° degree Fahrenheit rating of the UltraLite is pretty conservative. It is certainly on the warmer side of the 20°F bags available and is the warmest bag in our review. We slept in a 14F night with long underwear and a light fleece and were super comfortable when the draft collar and hood were properly cinched.
While we appreciate the extra space to roll around in or comfortably throw a thick jacket on while using the bag, which can be found in the The North Face Cats Meow and Kelty Cosmic Down. The UltraLite is a much more thermally efficient sleeping bag for average sized, or still even slightly larger than normal users. Remember that fit is a crucial component of a warm sleeping bag. The wider, "more-comfortable" bags have more dead air space inside the bag, resulting in a better chance for cold spots and the possibility of disrupted sleep.
The WM Ultralite was hands down the warmest bag in our review. Our testers even used this bag down to 14° without having to add that many layers and slept very comfortably.
Similar to the MegaLite, 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 less useful for keeping you warm on those hotter nights).
Very inviting lofty down and soft, lightweight 12D Extremelite fabric featured on the outside of the WM UltraLite. The fabric used on the inside of the UltraLite (and MegaLite) was our testers favorite for feeling the "coziest" and softest against our skin.
The regular length UltraLite weighs 1 lb 13 oz. It's nearly the lightest bag that is rated to a temperature of below 25°F (in our review) and is lighter than a majority of bags rated in the 30-35°F range (that are currently on the market). The exception is the Marmot Phase 20 which isn't quite as warm as the UltraLite but warmer than most other 20° F bags and is more compressible and an amazing 6 ounces lighter checking in at 1 lbs 7 ounces and is one of the better performing all-around bags in our review. Be sure to check out the chart below to compare the weight score of the UltraLite to the other bags in this review.
What's more amazing about the weight of the UltraLite is not only is it warmer than a majority of 20° and 25° bags we reviewed but in several cases, it was significantly warmer than these models.
At 1 lbs 13 oz, the UltraLite remains among the lightest bags in our review, and for cold sleepers or early season trips the UltraLite is more than reasonably weighted for even the most extended outings. Photo: The WM UltraLite out for an extended early season trip in the High Sierra.
The UltraLite uses "Extremelite," a 12D fabric for the shell, and is the same as our award winner, the Western Mountaineering MegaLite. Extremelite fabric weighs less than 1 oz per square yard, which is insanely light. The ultra-fine yarn that makes up this fabric is very soft and ultra-compressible. Albeit a little bit fragile, this very down-proof fabric greatly contributes to the bag's low weight and high compressibility. Another contributing factor to the low weight of the UltraLite is its slim cut, which is indeed one of the narrower sleeping bags in our test. Less material obviously shaves a handful of ounces from the overall weight.
The dimensions of the WM UltraLite are a little slimmer than several bags we tested. Here, the Ultralite (center) compared to the WM MegaLite (left) and the 20F Kelty Cosmic Down (right).
Comfort and Fit
High loft and soft, lightweight materials make the UltraLite a very inviting place to lay your head for the night, earning it an 8 out of 10 in this metric. However, the narrow shoulder and hip girth make it less comfortable than the MegaLite or Marmot Phase 20. Folks who mostly sleep on their back won't detect this as much, but for side and tummy sleepers, it is more likely to be noticed. Overall, the UltraLite and MegaLite offered the softest and most comfortable feeling face fabric out of all the bags that we tested. It is worth noting that the Marmot Phase offers slightly larger dimensions and feels slightly wider than the UltraLite.
The Kelty Cosmic Down and Sierra Designs Backcountry Bed are reasonably priced contenders that scores high in this comfort metric. If you're looking for an option that offers quality and comfort at a cheaper price point, consider these bags.
The WM Ultralite pictured in its included stuff sack. This stuff sack worked okay, but we could easily pack the UltraLite a 1/3 smaller with a compression sack.
Five inches of loft looks like a lot to pack away when this bag is laid out on your sleeping pad. However, the 850+ fill down and extremely lightweight materials make the UltraLite a much smaller package than you would expect, especially when stuffed into its included well-fitting stuff sack - or better yet, a compression sack.
The WM Ultralite (third from the left) offered one of the smaller packed sizes among any bag we tested, something that was particularly impressive because it was also the warmest bag we tested.
Despite being the warmest bag in our review, it was among the most compressible and packed down WAY smaller than all the 20F bags (and most of the 30F bags).
The included oversized storage sack for the WM Ultralite. This cotton bag was perfect for long term storage and helping to keep your bag lofty and performing well for years to come.
Features and Design
Wraparound baffles let you push down around to adjust your warmth. Move it to the top for cold nights, to the bottom for warm ones.
The above chart details each bag's score in the Features and Design metric.
The well-designed reverse differential hood on the WM Ultralite. Basically, the fabric on the inside of the sleeping bag is actually larger than the shell fabric resulting in a very comfortable and effective fit without needing to tighten it too much.
Similar to the AlpinLite, the UltraLite features a reverse differential hood, which is extremely comfortable. This hood covers your head, offering extreme comfort, and is excellent at trapping heat without needing to tighten it too much.
The WM Ultralite features a one-inch wide stiffening tape on both sides of the zipper that helps to aid in easy, snag-free operation.
Stiffening tape keeps the zippers running smoothly. The draft tube along the zipper and the draft collar on the UltraLite are lofty; they mate well, which keeps the 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. The draft collar, in particular, allows a minimal amount of cold air to enter the bag.
While there is a pretty big range in denier thickness among bags we tested, we didn't think that it greatly affected a bags durability, as sleeping bags (hopefully) aren't exposed to too many sharp objects or abrasions. Conversely, a lighter weight 10-12D shell fabric can weigh only a third of an average-weight bag using a 30-50D shell.
The UltraLite is among the most versatile bags in our review. It's capable of unzipping for warmer nights, but can be used in temperatures of 20F, as rated (and when sealed up). For sleepers that experience the cold sooner than others, or on extra cold nights, nearly all of our testers had no problem adding at least one lighter-weight jacket to boost this bag's warmth (if temps really got frigid). The continuous baffle design also lets the user further regulate temperature. The bottom line is even for the weight-conscious backpacker, this one pound thirteen ounce sleeping bag is very reasonable to carry and is certainly warm enough for the cold nights of the shoulder seasons or at higher elevations.
The North Face Cats Meow and Hyper Cat also score well for versatility. The Cats Meow excels on shorter backpacking trips, extended car camping trips, or adventures where you might expect to feel a bit of moisture. The Hyper Cat is light enough to go further and longer into the backcountry.
The WM UltraLite is a very versatile bag, performing well on both warm summer nights to shoulder-season alpine forays. Here we stayed cozy in the Western Mountaineering UltraLite even during a very cold late season rainstorm.
The UltraLite is one of the best sleeping bags in our review for 3-season use. Because it's so warm, it's best suited for travel in the mid to high elevations in the middle of the summer. It is also warm enough to stretch your season into the shorter days of fall and transitional periods in the spring. If you're someone who gets cold easily, the UltraLite could be your anytime, anywhere 3-season bag. It's plenty warm for most summer-time mountaineering in the lower-48 and lower regions of Canada and is light and compact enough for spring multi-day ski touring missions.
At $500, the WM Ultralite is on the more expensive side, but we still think its a good value if you can afford the initial investment. This made-in-the-USA sleeping bag (with the sewers names labeled here) uses the highest quality materials and craftsmanship and will easily last 15, 20, or more years and will perform well on an extremely wide range of trips.
One of the reasons that we prefer high-quality down sleeping bags is that they have a very long lifespan. Unlike synthetic fabrics, they can be stuffed and unstuffed over and over without breaking down the insulation. 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.
However, at around $525 for the regular length model, the UltraLite is a pretty big investment. But, if that bag can sustain 10-20+ years of use, and be your go-to for most of your backpacking trips, along with maybe the occasional mountaineering or ski touring adventure, we think that it is a good investment. You won't be disappointed by the UltraLite. If considering the Ultralite be sure to check out the similarly performing Marmot Phase 20 which is less expensive.
The WM Ultralite is a former Editors' Choice and remains a fantastic and versatile bag. The only reason it didn't win our overall Editors' Choice is that it's a little warmer than most people need for backpacking, and the MegaLite featuring less insulation compresses smaller and is 5-ounces lighter. However, for cold sleepers or colder than average conditions the UltraLite is tough to beat.
The UltraLite is a former Editors' Choice and remains a fantastic bag. It offers a few disadvantages, mostly revolving its slimmer-than-average fit, but is among the lightest, warmest, and most compressible bags for its temperature rating, similar to the Marmot Phase. The UltraLite wins our Top Pick for cold sleepers or "colder" 3-season use, as it is still noticeably warmer than the Phase. The MegaLite won our Editors' Choice over the UltraLite because it is a little more spacious; it also offers a 30°F rating that we think is warm enough and more appealing for most folks that are interested in backpacking bags. As a result of having less insulation, the MegaLite compresses smaller and is five ounces lighter. If you're a cold sleeper, the UltraLite is tough to beat for weight, packed size, the comfort of materials, and warmth.