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Western Mountaineering UltraLite Sleeping Bag: Long Term Gear Review

Western Mountaineering UltraLight on the Appalachian Trail
Western Mountaineering UltraLight on the Appalachian Trail

I’ve owned a Western Mountaineering UltraLite 20 degree sleeping bag for 4 years and I reckon I’ve backpacked over 1,000 miles with it. With an MRSP of $370, the UltraLite is one of the most expensive items I’ve ever purchased for backpacking, but it has proven its value repeatedly and with proper care, I expect it will last another 10 years.

If you’re not familiar with Western Mountaineering, they are considered one of the top sleeping bag manufacturers, with a worldwide reputation for making very lightweight and compressible bags using 850+ fill power goose down. Weighing just 1 pound 13 ounces, the UltraLite is one of the lightest weight 20 degree sleeping bags available and easily compresses into a 8 liter waterproof stuff sack when packed.

Fitwise, the UltraLite is one of the slimmest Western Mountaineering’s bags available with a shoulder/hip/foot girth of 59″/51″/38″. The narrow cut helps keep the weight of the bag down and makes it easier to warm up because there isn’t much free space inside it. The lightest weight sleeping bags have high fill power down and narrow dimensions like this.

The outer cover on the UltraLite is breathable lightweight nylon with a DWR coating. The DWR coating has broken down over the years and I need to reapply it the next time I give the sleeping bag a wash in a laundromat. Occasionally, the foot box will be a bit damp when I wake up, but I can’t tell if this is do to exterior condensation (I often sleep in a UL bivy sack) or interior perspiration by my feet. Regardless, it dries within a few minutes in the morning before I stuff the bag into its stuff sack.

In addition to the narrow fit, the UltraLite has a down collar the runs around the upper chest to prevent heat from escaping when you move around at night. The bag has a full zipper which is useful for venting in warmer weather as well as a down filled draft tube running the length of the bag to prevent side drafts. In addition, the baffles are continuous, making it possible to move down from the bottom of the bag to the top if more warmth is required or from top to the bottom where it will be compressed and not retain heat, in warmer weather.

Western Mountaineering UltraLight Sleeping Bag
Western Mountaineering UltraLight Sleeping Bag

Temperature-wise, I’ve had the UltraLite down into the low twenties without any issues and I feel that it’s temperature rating is true.

If there was one thing I could change about the UltraLite, it would be it’s weight and warmth. I often find it a little bit too warm in New England except in early spring or autumn. I bought this bag before I understood how to augment the warm of a sleeping bag by wearing additional cold weather clothing and I’d probably go for a Western Mountaineering  32 degree SummerLite, if I had a chance to go back 4 years in time.

However, I’m not ready to buy a SummerLite if I can avoid it and I still haven’t fully exploited the ability to move down away from the top of the UltraLite to its bottom using the continuous baffles. With summer on the horizon, I have plenty of time to see how these changes affect the UltraLight’s warm weather profile and temperature range.

Disclosure: The author owns this product and purchased it using their own funds.

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  1. Problem with the summerlite is it is snug and tight means the extra clothing would not loft that well. So the warmth gain could be restricted.

    Also the bag weight claimed is a way short of the truth. Better to get a Marmot Atom with more width and not a lot of weight gain.

  2. That is news about the weight of the bag. I'd never heard that about a WM bag. What is the weight if I might ask? I know you've owned the Summerlite.

    I've owned a Marmot Atom and the weight was off there too. Badly. The experience really poisoned my relationship with that brand.

    Measurement wise, the SL has the exact same measurements of my UltraLite, which I've worn extra clothes in, so I'm not understanding how the Summerlite would be all that different in fit. I figured it'd be the same.

  3. So i have been using a REI Sub kilo that I got for about 150$ in the online outlet good price for the weight and warmth. So far it has served my purposes and I have been thinking about upgrading.

    I have been thinking about making/buying a down quilt. Have you had any experience using one? I basically use the kilo as a quilt in spring summer. Just Unziped over the top of me.

    Used it like that last weekend at lake Colden and it got down to about 40 at night. Just not sure if i want to transition zipper-less and spend the time or money to make one if I'm not going to like it.

    I wish I had one to test first haha.

  4. I've resisted that transition because I like the enclosing feel of a mummy bag, even though using a quilt in the summer makes a lot of sense.

  5. Interesting that Martin mentions the Atom. I have one and honestly have never liked it. For me it doesn't seem to do anything well. When it is warm, the 1/2 zip prevents me from using the bag as a quilt or partial blanket. On the lower range I have found that the sewn-through vs. baffled design leaves cold spots (I tend to sleep cold) and I am uncomfortable at anywhere near its stated range. It has hung in my closet for several years.

    Two years ago I walked into one of those "OMG" moments when a store I visited was selling off their display WM bags and I found a Megalite on sale (almost unheard of). The Megalite has turned into my "do everything" 3-season bag and I can't say enough good things about WM. My current plans for the Atom is to convert it to a quilt, which will be my biggest sewing project to date. I am having trouble getting the nerve to start, but in the end hope it will be a good warm weather addition for summer. I want to test a quilt to see if I like it, and this seems like a good way to start with little investment.

  6. I have a WM Summerlite. Mine (6' 0" size) weighs 20 ounces, which is 1 ounce over the listed weight. Living in hot and humid Houston, I'm assuming that might be due to moisture in the down.

    I've worn a MB Alpine Light jacket or an ID PLQ jacket inside the bag with no problems.

    I find the Summerlite to be a versatile bag, and have used it down to temperatures in the mid/upper 20 degree (F) range.

  7. 603g vs the claimed 560g for the long. Atom was not much more. I recently sold both bags. Summerlite by the way on a long is claimed one inch wider on the website. I liked the summerlite but I am broad shouldered and tall. So extra clothing in it was compressed a bit. Don't forget the continues baffle is good but the stitching still goes through between chambers. Hold it up in sunlight to see were cold can get in.

    I also laid both bags together and the loft was comparable. Weight was measured from the shop. No humidity. Also BPL found it weighed more than claimed. Great kit but a little over priced and not all that was claimed when put under scrutiny.

    Katabatic quilt is spot on the weight claimed and the build and materials used rival WM all the way for me. Only issues there is the cord lock is starting to annoy the hell out of me.

  8. Last I weighed the Summerlite was last year with stuff sack…

    19.2 ounces

    I really only use it in the shoulder seasons & have moved on to a synthetic quilt for summer (MLD Spirit).

    Just FYI

  9. I'm not that tempted by a quilt yet. Good feedback on the Katabatic too. I'll keep your feedback on the Summerlite in mind. For the moment, we have a spending freeze anyway. I'm getting by fine with a 13.5 oz MontBell UL Spiral Down Hugger Thermal Sheet rated to 50 degrees (F). I can use it as a quilt (full zip).

  10. Hi,

    I am looking for a good 3 seasons sleeping bag. I am torn between Montbell ul spiral down hugger #1 and a bag from Western Mountaineering. At first I considered Versalite but I worry that it might be an overkill. What it the lowest temp. rating that you would recommend so I can not only extend my seasons but be reasonably comfortable in summer with the bag opened up as well?

    I have considered Ultralite as well but there are enough people complaining about it being too snag (especially when wearing extra clothing) too make me nerves about this choice. Fortunately I have discovered Alpinlite which is exactly the same bag but just 3 inches wider. I am 49” (across my chest including my arms) my husband is 51”. I believe that someone told me somewhere you need extra 12”. Therefore I should have a 61” bag and my husband 63”? That being the case we should both go for the wider Alpinlite? What do you guys think? Is my reasoning correct?

    Also I am 5’6”. Should I go for the 6” bag?

    Thank you in advance.

    Great website BTW. I have bookmarked you.

  11. I'd say the lowest temp rating should be the average temp of the locations/regions where you plan to camp and in the months you plan to camp. You can find this out by looking up the historical temperature records at wunderground.com. I don't believe that there is a blanket recommendation that anyone can really make – I have no idea where you are.

    As for size/width, it really depends on how warm you want to be: a Narrower/shorter bag will be warmer. I recommend that you buy some of your leading options from a retailer with a liberal return policy or go to the store and try them on. EMS has western mountaineering bags in their stores, for example.

    Sorry, I can't tell you what to buy. There are a lot of variables to consider. However, with the unlimited return policies offered by most online retailers theses days, you can test things out at home before making your final decision.

  12. Hi Earlylite,
    Thank you for your response. I forgot to mention in my last post that I am in Southern Ontario but eventually I would be backpacking all over the place (hopefully other continents as well) so I cannot say what will be the lowest or the highest temp. that I will likely encounter.
    I have just compared the WM bags again and I noticed that the Versalite is only 1 oz heavier than the Aplinlite but it takes me to lower temp. so I am tempted to get it. What would you do if you were me?
    Would a narrower/shorter bag be much warmer or just somewhat warmer?
    I will most likely be ordering from the US so if I can I want to avoid returning stuff.
    Thank you.

  13. Southern Ontario…I'd get the WM Ultralite. I has the best temperature range. Getting a lighter bag with a higher temp rating will reduce your options if you plan to backpack all over and all year, with the exception of winter. That'd be my choice.

  14. In response to Martin Rye saying the SummerLite was over claimed weight, 603g is almost exactly what Western Mountaineering claims. 603g is 1lb, 5.27oz, and WM has always claimed 1lb, 3oz for the regular and 1lb, 5oz for the long, so I'm not sure why he's bothered. WM has never listed 560g for the long.

  15. 200 152/130/97 295 g 560 g 15 x 30 XXS

    Straight from the website for the Summerlite Bill. Seems they do claim 560g for the Long. if you don't believe me go look yourself. I am always going to read the metric weights. We left feet, pounds ounces behind years ago in Europe.


  16. I have owned a Ultralite for some time. Old listing weight when I bought it from IME was 26 oz., price was about $155 new (Caught Rick at IME in a clear out the inventory mode!) I am 5'7" about 175lbs. Love the Ultralite & have used in well down into the 20's. Also own a highlite short which weighs in at about 17 oz. (Ultralite weighs in at 29oz.) I don't trust the 35 degree rating on the Highlite & don't like the half zip. Have just ordered another Ultralite from IME for my wife as well as a Summerlite for me. We will start our AT trip March 24 next year with the Ultralite's & probably switch to the lighter bags after Mount Rogers in May. I also own a Sierra Degigns Wicked Light as well as an old Sierra designs 200, an old EMS 100 & a Marmot Bag. (The Marmot was a lost & found when I worked for the AMC at the Crawford Depot). Just sold old winter Twin Peaks bag on consignment at Ragged Mtn. & will be selling old Snow Lion winter bag there after I wash it. I feel that WM makes some of the best bags out there plus IME is always great at backing what they sell. Also ordered 2 pairs of the WM Flash pants & 2 pairs of WM down booties, figure they will extend temp ratings if needed.

  17. If you had a choice between the Summerlite and the Super Spiral Down Hugger from Montbell, is there a clear choice? For mostly mid-spring to mid-autumn backpacking in New England (plus a brief stint in Denali late September). Summerlite being 1lb 3 oz, and Montbell at 1lb 6 oz, so weight doesn’t seem much of a variable. I’m curious if either seems to be more true to its temperature rating than the other, or if there are quality preferences for folks. Many thanks as always for an advice.

  18. One could argue that the super spirals are better for side sleepers. If it were me, I’d go with the Summerlite. WM bags tend to be very true to temp ratings – I don’t know about Montbell but they also have an excellent reputation.

  19. Can you tell me what outer-shell and pad you are using with your bag? I think I am going to go with the Megalite – for extra room. Have you used any additional “liners” inside the bag? Thanks for the information and advice.

  20. I’ve got the MF shell and I’ve since switched to a Thermarest Neoair Xlite.
    Here’s a description of the different shell fabrics WM offers on their bags.
    MF is the way to go in my opinion.

  21. Hello Sir,

    I like your website very much, great in-depth, honest reviews. I have a question I hope you might be able to answer. I am debating between purchasing a WM Summerlite and a WM Ultralite primarily for 3-season use. This summer I will be attempting a thru-hike of the JMT (in August). If I’m using an Exped Synmat 7, do you think the Summerlite will be warm enough? (I have read that even in August temps can hit 20 or below). I will also have baselayers (capilene) and a down sweater available if layering is necessary. I ask this because I read above you note the ability to layer for colder temperatures.

    I appreciate your input.



  22. Have had a WM summerlite bag for about 8yrs, 6’6″ length. Not sure of current price at Paddy Pallin but back in 2008 it cost $679.95 Australian! When the temps get down to 0C it’s rating (lower limit) I need extra clothes on. Due to it’s narrow construction I’ve started using it as a quilt after buying a Neo air X lite mattress and this has made a huge difference in comfort. The only thing I have a prob with is, as a side sleeper the down slides off my shoulder and hip leaving them cold, so several times a night I must push the down back into place and all is good again. Along with my silk liner and S2S silnylon stuff sack it weighs 807g. So far there is no material or workmanship issues.

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