For many lightweight and ultralight backpackers looking for a single sleeping bag to suit their needs throughout the year in many parts of the country, a 20 degree bag is often chosen for its blend of warmth while still remaining light enough to easily carry. Here in the Rockies, it might be a bit too warm in the summer, though you’ll still see lows in the 20’s at times at high elevation even in August. For spring and fall the rating is nearly spot-on perfect, and for colder temperatures you can always layer by wearing extra insulation within the bag to push the bag below its rating provided that conditions aren’t too extreme. Of course, it can be nice to have the luxury of several bags to choose from depending on the situation, but for many of us the 20 degree bag makes for an excellent all-around choice.

Western Mountaineering (WM) offers two 20 degree rated bags to fit this niche – the standard UltraLite and very similar but wider and more roomy AlpinLite. Founded in 1970, San Jose California based Western Mountaineering have been manufacturing high quality down sleeping bags and garments that frequently make the short list of any buyer interested in the warmest, lightest, and most packable down gear available. As you might expect with a product that competes among the best of the best in these categories, Western Mountaineering products often come at a price – in the $600 range for the 20 degree UltraLite Sleeping Bag reviewed here. WM fans will tell you that few can compete with the package you’ll receive, however, and in this review I’ll take a look at the UltraLite and share my experiences after several years of extensive field use.

The Western Mountaineering UltraLite is a lightweight, packable down sleeping bag that is made in the USA of ethically-sourced premium goose down.

Specifications & Construction

The UltraLite is a mummy-shaped bag available in the following lengths, with the corresponding weights as stated by the manufacturer:

• 5’ 6”: 1lb 12oz
• 6’ 0”: 1lb 13oz (1lb 13.6oz measured)
• 6’ 6”: 1lb 15oz

I tested the 6’ 0” model of the bag, which came in at 29.6oz on my scale. Both the short and medium length share a 59” / 51” / 38” shoulder / hip / foot girth measurement, with the long model gaining an inch in the shoulder and hip areas. You might notice that this bag is a tighter fit than many competitors – WM has elected to keep the fit like this both to minimize weight as well as keep the temperature rating of the bag low without having to add more down. If the bag were larger, more down would be required to maintain the same temperature rating due to the dead air space.

Speaking of down, 850 plus fill power goose down is used for insulation. Fill weights start at 15oz for the short model, and go up 1 ounce each for the medium and long lengths. According to Western Mountaineering, this amounts to 5” of loft, accurate per my measurements. A down-filled hood and collar seal in the heat and continuous baffles (as opposed to sewn-through construction) help eliminate cold spots. The bag is part of WM’s “ExtremeLite Series”, which feature very lightweight shell materials with a DWR treatment. There’s no color choice – the outside is a deep blue color with a black bottom and inner lining. The bag has a full-length zipper with a separate slider on the foot end to allow for ventilation as needed, and a down-filled draft tube inside protects the zipper area from wind and heat loss. The bag is offered in both right hand as well as left hand zip models. All of this packs down into a 7” x 13” package. If you’ve looked around, you’ll know that a 20 degree bag managing to stay under the 2lb mark is hard to find.

The UltraLite's loft measured at 5” in my testing.

Impressions & Field Use

If you’re not buying from a brick and mortar store, the bag will be shipped uncompressed in a large box so there’s no worry of compromised loft. The hand of the fabric is crisp yet soft to the touch, and the bag seems to explode into space from the substantial amount of down fill. When new don’t be surprised if the bag sheds a few feathers that sneak through the fabric with sharper quills. These can be carefully worked back into the bag if they haven’t completely come through the fabric using an inch-worm technique if desired, but the great majority of the insulation is soft down that won’t be able to exit the bag. The sewing and construction is second to none, and after handling the bag you get the idea that WM really cares about the products they produce.

The fit is on the slim side and as a 180lb side-sleeping tester who normally wears a men’s size medium to large t-shirt, I felt the bag worked and was warm and comfortable, but there was little room left to layer for colder conditions. It seems that this weight range / size is about the upper limit for use of the UltraLite in comfort, and the bag is ideal for trimmer users. A lot of this comes down to personal preference of course – a larger bag will give you more room to move and to layer, but will be heavier and dead air space within a bag isn’t a formula for warmth. Another thing to consider is how you sleep. If you’re lucky enough to be a back sleeper that rarely moves during the night, you’ll probably be able to get away with a tighter fit and remain comfortable.

Due to its down construction, the UltraLite packs down to a respectable size.

Western Mountaineering includes a standard nylon stuff sack, but I prefer to keep my critical sleeping gear in an ultralight dry sack for peace of mind. I found that I could get the bag into a 8L dry sack with a bit of effort, but moving up to a 13L size eliminated a bit of stuffing frustration and didn’t compress the loft quite as much on the trail. Arriving in camp the bag quickly attains full loft after being unpacked with a bit of coaxing – a quick shake here and there will help move things along. The baffles are continuous – if needed, you can shake the bag side to side to move down from the bottom of the bag to the top as needed for a little temperature control. The down on the bottom of the bag has little insulation value once compressed by your weight.

Once inside, the bag drapes over your body comfortably, and you can immediately feel the down start to work its magic and trap your body heat. If you get too hot, the full length zipper and separate foot box slider allow for plenty of ventilation options. WM has sewn in a stiffener along the zipper in an attempt to minimize zipper snags (more on that later), and the down-filled draft tube does a good job of preventing a cold spot along the zipper during cold and / or windy weather.

On the warmer nights, the bag works great as a quilt as well – just unzip completely and use the foot box to keep the bag in place. Without the hood and draft collar engaged, and using an appropriately warm sleeping pad for the conditions, I found the bag to be warm to around 40 degrees. Beyond that temperature, the down-filled draft collar, operated by an elastic cinch cord and cord lock, really helps to seal in the heat around your body and prevent the billows effect – where moving around pushes all the warm air out of the bag, leaving a chilly sleeper behind. To reach the 20 degree rating, full deployment of the draft collar as well as the hood (operated by a non-elastic cinch cord and cord lock) will be required. In this mode, you are completely sealed inside the bag save for just a small hole that allows you to breath.

I’ve used the Ultralight in cool to cold conditions during dry as well as humid weather at both high and low elevations, and dressed in normal base layers without adding additional insulation, I found the 20 degree temperature rating to be accurate. You may however, start to feel an occasional chill as the temperature drops to around the 25 degree mark, especially if you move a lot in your sleep. Wearing extra insulation inside the bag, such as a down or synthetic insulated jacket and pants, can help boost the comfort level considerably, especially if the tight fit of the UltraLite allows you to do so without compressing the insulation of the extra clothing or the bag itself. Jen, as a self-confessed cold sleeper, had similar experiences with the bag, but found a 5-10 degree difference in her case – feeling chilly as temps dropped below 30. She also hopes that at some point, WM will offer a women’s specific cut, as the UltraLite’s fit, while quite workable in her case, seems to be optimized for a man’s shape with broad shoulders and narrower hips.

The DWR treatment held up well to condensation, dew, and light overspray into the shelter from heavy rain, and I never had an issue with the down insulation being compromised due to moisture, even in very humid environments. Western Mountaineering states that extra care should be taken due to the lightweight fabric that’s used for their ExtremeLite Series, but the bag has held up very well without special care – although the bag was always used either inside a tent, shelter, or under the stars with a groundsheet. After spending a lot of time in the bag, dirt and oils from your skin will start to effect the loft and warmth, but a quick wash with a down-specific soap and a tumble dry on very low heat with a couple tennis balls tossed into the dryer solved that issue. If you need to reinforce the UltraLite's water resistance after washing, you can apply a spray-on water repellent at home. When not on the trail and in your pack, store the bag uncompressed in a dry place to maintain loft – Western Mountaineering includes a large cotton storage bag for this purpose.

I did have two minor gripes about the bag. One is that when the hood is cinched down, the cinch cord has an annoying tendency to hang down right in your face unless specifically placed out of the way. The other issue is that that even with the sewn-in stiffener along the zipper, I still had issues with it snagging on the shell fabric unless care was exercised.

The UltraLite's zipper does require some thought to prevent snagging on the lightweight shell fabric.

Conclusion

Overall, it’s hard to beat the quality of Western Mountaineering and they are frequently the yard stick that all other sleeping bags are measured against. The UltraLite doesn’t disappoint, and though the price is steep, as a down-filled bag it should last you long into your hiking career with proper care. Depending on your build and sleeping style, it may be a tight fit for many and if you fall into that category, the wider AlpinLite, the 30 degree MegaLite bag, or the 10 degree VersaLite bag may be a good choice. At times I was annoyed with the zipper and hood design, and at this price point I’d like to see little things like that just work. Unfortunately no women’s specific model is offered. In the end however, it’s hard to complain when you’re warm into the 20’s with a bag weighing less than 2 pounds.

The Western Mountaineering UltraLite is currently available in 3 sizes and retails for $600-$635. You can find it here at Backcountry.com.

Editor’s Note: This article originally appeared in Issue 5 of TrailGroove Magazine. You can read the magazine article here featuring the Western Mountaineering UltraLite rating, pros and cons, and more.