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Western Mountaineering Summerlite Sleeping Bag REVIEW

Hooded, down mummy bag rated to freezing that weighs a mere 19 ounces.

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by Don Wilson | 2006-12-19 03:00:00-07

Western Mountaineering Summerlite Sleeping Bag REVIEW - 1


Western Mountaineering introduced the Summerlite sleeping bag to the US market in January 2006. With features focused on three-season performance and light weight, it instantly drew attention from ultralighters. The Summerlite is the lightest fully baffled bag in Western Mountaineering’s lineup. It has a full-length zipper, insulated draft tube, 4 inches of double-layer loft and weighs 1 pound 3 ounces for the regular length. The long length bag has a specified weight of 1 pound 5 ounces (1 pound 5.4 ounces as measured). The Summerlite is part of the Extremelite series and uses a 0.9 oz/yd2 Extremelite shell fabric. In 2007, Western Mountaineering will offer a new short length version designed for people 5 feet 6 inches or less. This version will likely come in near a scant 1 pound 1 ounce. I used the Summerlite for 6 weeks on the Pacific Crest Trail this summer and have some strong opinions about its combination of features and performance. The picture at right was taken on a winter trip in Aravaipa Canyon, Arizona.

The Summerlite has an interesting history as described by Gary Petersen, Production Manager for Western Mountaineering. This bag was originally developed at the request of a European dealer who is a long time customer of Western Mountaineering. The dealer approached Gary in 2002 with a request for a very specific bag - a 32 degree F bag (0 C), in a narrow mummy configuration with a full-length zipper and a target weight of 1 pound 3 ounces (550 grams). They initiated production of the bag in 2003, but did not make it available worldwide until January 2006. It was immediately popular and is already one of the top ten selling products for Western Mountaineering.

What’s Good

  • 1 pound 3 ounce sleeping bag with three-season warmth
  • Full zipper is convenient and improves versatility
  • Baffled construction, an unusual feature at this weight, reduces cold spots
  • Narrow mummy configuration with hood
  • Stuffs into 12 by 6 inch stuff sack

What’s Not So Good

  • Might be a little narrow for some



2006 Western Mountaineering Summerlite


Mummy (with full length zipper)


9 oz (255 g) 850 plus down (regular length), 10 oz (283 g) for long length

  Measured Loft

2.1 in (5.2 cm) single layer with down distributed evenly across the bag (continuous baffles allow loft to be adjusted); 4.1 in (10.4 cm) double layer averaged from measurements taken at the shoulder, hip and 16 inches above the footbox

  Manufacturer Claimed Temperature Rating

32 °F (0 C)


1 lb 3 oz (538 g, regular length), 1 lb 5.4 oz as measured, (606 g, long length)


Regular (to 6 ft, 1.82 m), Long (to 6 ft 6 in, 1.98 m), Short length (to 5 ft 6 in, 1.68 m) available in 2007


0.9 oz/yd2 (31 g/m2) Extremelite 20D nylon shell


Insulated draft tube, full length zipper, drawcord and hood, 5.25 in spacing continuous baffles


$280 (Regular), $295 (Long)


The Summerlite is intended to provide the most efficient warmth possible in a full featured three-season sleeping bag. It offers a full zipper to help regulate temperature on those warm summer nights, but with a full hood and insulated draft tube, is still efficient when pushing the bag’s performance into colder temperatures. I used my bag in a broad range of three-season conditions; winter nights in the desert, warm summer nights in the desert and foothills, and cold, wet alpine camps. I found the Summerlite to have a well chosen combination of features and efficiency. I have not developed a liking for top bags or quilts, and the Summerlite is the lightest and most versatile mummy bag I have used - and it can be used in the vast majority of conditions that I encounter.

Western Mountaineering Summerlite Sleeping Bag REVIEW - 2
The size long Western Mountaineering Summerlite has plenty of room to cinch up the hood for the author, who is 6 feet 4 inches tall. The hood is comfortable and easy to operate from within the bag.

Western Mountaineering Summerlite Sleeping Bag REVIEW - 3
For cold nights, the hood cinches up easily, but still leaves access right where you need it. There is no neck collar on the Summerlite.

The Summerlite is the lightest baffled bag made by Western Mountaineering. The baffles are continuous and wrap around the bag. With a little practice it is possible to move more down onto the top side of the bag, improving effective use of the down. This is easily done by unzipping the bag and pushing the down along the tubes from one side to the other. The baffled construction is a real advantage over sewn through construction, reducing cold spots and improving overall warmth. The baffles on the Summerlite are spaced 5.25 inches apart.

Western Mountaineering Summerlite Sleeping Bag REVIEW - 4
The Summerlite stuffs in a conveniently small volume. My sample bag is a size long; other sizes will of course stuff into even smaller volumes.

Western Mountaineering Summerlite Sleeping Bag REVIEW - 5
Baffled construction keeps the loft of the Summerlite nearly uniform across its length. Average double-layer loft on my test bag was just above the specified loft of 4 inches.

The Summerlite is cut in what Western Mountaineering refers to as a narrow mummy configuration. The internal girth dimensions are listed as 59 inches at the shoulder, 51 inches at the hip and 38 inches at the foot, for the regular size bag. These dimensions are identical to those on the Highlite and Ultralite models; two of the other lightweight bags offered by Western Mountaineering. I am used to mummy style bags and found the Summerlite to offer plenty of internal room. But I am also more lean than most. The Summerlite fits the description as a narrow mummy - if you aren’t a fan of mummy bags, the Summerlite may not be the best choice for you.

Western Mountaineering Summerlite Sleeping Bag REVIEW - 6
The draft tube on the Summerlite is stuffed with plenty of down to eliminate cool spots along the zipper. The #5 YKK zipper is light, reliable and is less abrasive than heavier zippers when material gets caught in the zipper.

The exterior shell on the Summerlite is Western Mountaineering’s Extremelite fabric. When developing the Extremelite fabric, Western Mountaineering looked for a combination of light weight, strength and uniform yarns that would make the fabric as downproof as possible. This fabric is a 0.9 oz/yd2 Pertex Quantum which has been calendared (heated and pressed between rollers or plates to smooth and glaze the fabric) on both sides. This sacrifices some breathability, but also reduces down leakage. According to Gary Petersen, uniform yarn sizes reduce down leakage since any junction where yarns of differing diameter meet is a likely spot for leakage. Ripstop fabrics have regular intervals with yarns of larger diameter, which improves strength, but can lead to leakage. That is why Western Mountaineeing has both sides of the exterior fabric calendared. The interior fabric on the Summerlite is a plain weave with uniform yarns (taffeta). By design it is more downproof, and is therefore calendared on only one side. It is likely that Western Mountaineering will use up their current supply of shell fabric and switch to new shell fabrics sometime in 2007. Any new fabrics will have similar construction and characteristics as the current fabrics.

Over the course of the summer I have spent more than 50 nights in the Summerlite and I have experienced almost no down leakage. The shell fabric is very light and I treat it carefully, especially if I drape the bag over bushes or grass to dry it out. I make sure to pay attention when I remove the bag from these situations, not dragging it across branches where it could get snagged or torn.

Missing from this review (and for all sleeping bag reviews published here, for that matter) will be an assessment of whether or not the sleeping bag performs adequately at temperatures near its manufacturer-reported temperature rating. Click here for the complete Backpacking Light Position Statement on Sleeping Bag Temperature Ratings.

What’s Unique

The Western Mountaineering Summerlite is a top quality, 19-ounce (regular size), 32 degree traditional mummy sleeping bag with a full zipper, draft tube and continuous baffles. No other bag on the market offers this combination of features and light weight. The Mountain Hardwear Phantom 32 and The North Face Beeline are similar (and a little less expensive) but the Phantom has box baffles and a three-quarter zip, while the Beeline has no zipper except for a foot vent. Nunatak presents a third option in the Alpinist which has a half-length center zip and 2.5 extra ounces of down for an extra $100.

Recommendations for Improvement

The Summerlite hits the mark for a very lightweight yet versatile three-season bag. Western Mountaineering has sacrificed some breathability to reduce down leakage by using Extremelite fabric. If they can find a fabric that combines improved breathability with similar downproof performance, the Summerlite could take another step forward.


"Western Mountaineering Summerlite Sleeping Bag REVIEW," by Don Wilson. (ISSN 1537-0364)., 2006-12-19 03:00:00-07.


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Western Mountaineering Summerlite Sleeping Bag REVIEW
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Benjamin Smith
(bugbomb) - F - M

Locale: South Texas
Western Mountaineering Summerlite Sleeping Bag REVIEW on 12/19/2006 22:48:01 MST Print View

Companion forum thread to:

Western Mountaineering Summerlite Sleeping Bag REVIEW

Brett .
(Brett1234) - F

Locale: CA
re:Western Mountaineering Summerlite Sleeping Bag REVIEW on 12/19/2006 23:28:53 MST Print View

I wish I had a WM bag in my kit [note 'ars3nal' was considered profanity!? huh??]; maybe some day. For those few hikers like me who do not like the feeling of a tight mummy bag and like to stretch, roll around, cross legs, etc.. MontBell might be an option. It was my choice; 'stretch baffles' constrict gently to maintain maximum loft, or expand to give 75% more internal volume (compared to this Summerlite). Stretch baffles also automatically make more room for extra layers, such as a synthetic lofting pants/jacket combo, without compressing it much.
1lb 7oz for a 0'bag:

Ryley Breiddal
(ryleyb) - F - M

Locale: Pacific Northwest
Megalite! on 12/20/2006 11:47:21 MST Print View

The WM Megalite is the marginally heavier, more roomy version of this bag. I'm not "lean" like the author, so that pretty much made the decision for me as far as one vs the other :)

Don Wilson
(don) - MLife

Locale: Koyukuk River, Alaska
Re: Megalite! on 12/20/2006 12:02:35 MST Print View

Yes, the Megalite is definitely an option if you want, or need, the extra room. The only other difference (besides dimensions) between the Megalite and the Summerlite is that the Megalite has a neck collar, while the Summerlite does not.

paul johnson
(pj) - F

Locale: LazyBoy in my Den - miss the forest
Re: re:Western Mountaineering Summerlite Sleeping Bag REVIEW on 12/20/2006 12:09:55 MST Print View

Brett, i have a WM Highlite - short length bag. excellent bag in quality of construction and performance.

has a few weak points on design however, viz. poor hood design, wt. saving half-zip makes getting into the bag (particularly when in a tight bivy sack) a bit of a challenge (but all that wriggling activity contributes to initial warmth!!), quite tightly cut - again to save weight and increase warmth of the 7oz of down fill. i'm not going to get into diffs b/t MB 725FP down and WM 850FP down. if interested, search the Forums, this has been discussed a number of times.

i have come to prefer the MB SS bags to the WM Highlite.


a) well, of course the SS system
b) full zip
c) much better hood
d) perhaps better for extending range by wearing high loft insulating jacket due to the SS system. in fact, when wearing hi-loft ins. jacket, the MB bag might actually be warmer than the Highlite since the SS permits wearing the jacket with little or no loss of loft of bag or jacket (admittedly, this is more of an assumption on my part, because while i've done this, i really haven't done side-by-side comparison testing). in the Highlite, it is a tight squeeze even w/o wearing a high loft jacket to increase the temp range, hence my prev. assumption that wearing a BMW Cocoon inside of the Highlite will result in compression of the insulation of either the jacket and/or the bag (so, will there be any net gain in insulating ability???).

downside of the MB is the few ounces of extra weight of the MB bag in order to get a somewhat similar temp rated bag - again, though, this might be offset a bit if using a lighter MB bag and wearing a hi-loft layer in the MB bag.

Tom Clark
(TomClark) - MLife

Locale: East Coast
Re: Re: re:Western Mountaineering Summerlite Sleeping Bag REVIEW on 12/20/2006 17:58:54 MST Print View

I am 5'6" and 160 lbs. I have the regular length AlpineLite which is a wider version of the UltraLite Super (both 20 deg F bags), thinking that a little extra room would be nice for additional insulation (down jacket or summer down bag on really cold nights) and storing shoes and water bottles inside. At times I have wished that I had gotten the 5'6" UltraLite version since my feet have felt cold, and the extra width has left me feeling cool...even with the legendary understating of WM bag temperatures. Sometimes there is just too much space. However, when I was shopping for the bag the UltraLight did seem a bit too tight.

Has anyone else had trouble with limited space or excessive compression on the narrow WM bags?


Phil Barton
(flyfast) - MLife

Locale: Oklahoma
Re:Western Mountaineering Summerlite Sleeping Bag REVIEW on 12/20/2006 21:36:41 MST Print View

Tom, I'm not quite as slim as I should be at 6' and 205#. I have the WM HighLite. It too is a slim cut bag. Measurements are listed by WM as shoulder - 60", hip 52", and foot 38".

It is snug. I've only had 2 nights out where I've needed to wear insulation to bed using a GoLite Coal jacket with hood. I would say that I don't have a 1/2" to spare. Another couple of inches in the shoulders and hip would feel better to me. I don't know that it would make the bag perform any better. I agree with WM's claim that the MegaLite warms quickly.

As PJ pointed out the hood could be a little better. But overall, I'm pleased with the weight and great warmth of this bag. My long bag weighs 16.9 oz. There have been some compromises to make it this light -- a short zipper and no draft collar for instance. Those are OK for what I seek in a 3 season bag.

Randy Brissey
(rbrissey) - M

Locale: Redondo Beach, CA
PCT Warmth on 12/20/2006 21:38:09 MST Print View


Did you have any problems with your legs (the feet specifically) getting cold at night in the Sierras. I see that most of your insulation is torso and head and wondered without insulation under the feet did you have a problems?


Don Wilson
(don) - MLife

Locale: Koyukuk River, Alaska
Re: PCT Warmth on 12/20/2006 21:47:39 MST Print View

Randy -

I had no problems with warmth at all. In the Sierras I frequently camped low, at 8000 or 9000 feet, but I did spend a few nights at or above 11000 feet. Sometimes I'd put my pack under my feet, more for comfort than for warmth. The footbox on the Summerlite is nice and square, and well filled with down. It is a darn good bag - though I have not tried the MB stretch bags.

Randy Brissey
(rbrissey) - M

Locale: Redondo Beach, CA
Marmot Bags on 12/20/2006 22:04:02 MST Print View


Have you used any of the lighter bags from Marmot and if you have how do they compait to WM's?


paul johnson
(pj) - F

Locale: LazyBoy in my Den - miss the forest
Re: Re: Re: re:Western Mountaineering Summerlite Sleeping Bag REVIEW on 12/21/2006 03:54:06 MST Print View

Thomas, i too am a wide-body, albeit a very short wide-body. i can use a WM Highlite - short length, which is a very fine bag (both in quality of construction and performance), but can barely move inside, making zipping/unzipping downright difficult. The tight lower body is fine, it's just that, IIRC, 59" shoulder girth. Also, WM is generally spot-on in their claimed lower temp ratings, and i consider myself a cold sleeper (though i need non-hi-loft layers to get to the Mfr. claimed lower limit of range).

i prefer the Montbell SuperStretch bags over my WM bag. However, to get equivalent warmth in an MB vs. WM bag, the MB will weigh more, IMHO.

The MB SS system will avoid the cold spots that might be caused by larger air volumes next to your body. It also allows ease of movement inside the bag while excluding the extra air next to your body, even at your feet - sort of a "win-win" situation.

Figure a MB SSDH #3 will be 23oz with 0.5oz more down (lower fill power, but let's not get into that issue here) as cp. to the WM Summerlite.

The SS system allows shoulder girth ranges, IIRC, from ~53" to ~71" with its GENTLE, non-compressive SS system. It's very easy to layer a hi-loft jacket (and pants, if so desired) to extend the range of the bag w/o compressing either the hi-loft clothing or the bag's insulation. Under these circumstances you might be able to take a slightly heavier (than its WM counterpart) down further than you would with the tighter fit of WM. Though as Shawn Basil has recently pointed out in another Thread, he achieves better results by laying his hi-loft clothing on top of his bag to extend the range, thereby eliminating compression and loss of loft.

The SS system avoids the issues some people have of a roomier cut WM bag and heating that extra air, particularly at the footend.

MB prices are comparable to WM prices.

Just a thought.

Don Wilson
(don) - MLife

Locale: Koyukuk River, Alaska
Re: Marmot Bags and a question for readers on 12/21/2006 09:51:03 MST Print View

Randy -

I have a Marmot Atom that I am testing now. I did a short Spotlite review on it a few weeks back - look over at the spotlites.

The specs on the Atom are very similar to the Summerlite. But the Atom uses sewn-through construction and has a half zipper. I've got more testing to do before I weigh in on the comparison between these two bags.

I may do a side by side comparison article in 2007. I am specifically interested in the performance differences between the baffled construction of the Summerlite and the sewn-through construction of the Atom. It is the collective common wisdom that sewn-through construction creates "cold spots" or is generally inferior. But how much? Is this really significant? Do other aspects of construction and design overcome these differences? I'm working on some ways that we might be able to quantify and test this - specifically by comparing the performance of the Summerlite and the Atom in some type of controlled test. No guarantees yet that we will be able to complete that test - but it is under consideration.

Would you readers find that comparison interesting?

paul johnson
(pj) - F

Locale: LazyBoy in my Den - miss the forest
Re: Re: Marmot Bags and a question for readers on 12/21/2006 09:57:32 MST Print View


[BT, how's that for a short post!!!]

Randy Brissey
(rbrissey) - M

Locale: Redondo Beach, CA
Atom Vs Summerlite on 12/21/2006 10:28:54 MST Print View

Hello Don,

What I saw recently that interested me was that someone had placed two different sleeping pads on top of a thermal imaging sensor so that you actually see that cored foam did leak heat more than a solid sheet. I would like to merge the two ideas together and be able to see where sleeping bags leak heat and how much of a difference draft collars and hood openings help conserve heat.


Don Wilson
(don) - MLife

Locale: Koyukuk River, Alaska
Re: Atom Vs Summerlite on 12/21/2006 11:21:12 MST Print View

Randy -

You nailed it. That's exactly what we are looking at doing. But if we do that, we'll try to keep it controlled enough to make the data valid. Otherwise, we probably won't do it.

PJ - Impressively short post. You've left little room for future brevity improvements :-)


Edited by don on 12/21/2006 11:22:20 MST.

Richard Nisley
(richard295) - M

Locale: San Francisco Bay Area
Re: Atom Vs Summerlite on 12/21/2006 11:22:26 MST Print View

Randy-There is an alternative source for the information you are seeking, if they sell their bags to EU countries. If they do, ask the vendors for a copy of the Informative Appendix for their bag's EN 13537 Test. Non uniform heat losses are clearly quantified by the 20 manikin segments.

Edited by richard295 on 12/21/2006 11:28:31 MST.

Randy Brissey
(rbrissey) - M

Locale: Redondo Beach, CA
Sleeping Bag Info on 12/21/2006 11:49:08 MST Print View

Thank You, Richard

Mitchell Keil
(mitchellkeil) - F

Locale: Deep in the OC
Re: Re: Marmot Bags and a question for readers on 12/21/2006 12:15:54 MST Print View

I would be interested in a side by side by side comparison with the MB SS #4 rated to 37 degrees. Sewn through vs baffled vs SS with compartmented baffling. The weights of these bags and prices are close enough that most of us would, I think, consider each in a purchase decision matrix. When I hold my MB bag up to bright sunlight I can see how they have constructed the individual squares for max loft to work with the SS system. Very impressive. And for those of us who take your caution that if you are not slim or a toss-n-turn sleeper an altenative should exist to the narrow cut mummy.
Check my User Review of the MB SS#4 bag which I updated.

Edited by mitchellkeil on 12/21/2006 12:18:31 MST.

paul johnson
(pj) - F

Locale: LazyBoy in my Den - miss the forest
Re: Re: Re: Marmot Bags and a question for readers on 12/21/2006 12:58:31 MST Print View

I think that the MB SSDH #3 is a better match when comparing against +30-32F rated bags, since the MB SSDH #3 is rated to +32F. Sure it's heavier, but also has 9.5 vs. 8.1 oz of down (the Summerlite has 9oz - if i remember the review spec correctly), and i'm not sure that the #4 will perform well, but then, i'm a cold sleeper.

However, comparing similarly Mfr rated bags (hence the #3 vs. the #4 in this comparison) is probably the way to go.

Ideal would be to compare BOTH the #3 AND the #4 with the Atom and Summerlite.

Do you disagree Mitchell? If so, please let me know.

Edited by pj on 12/21/2006 12:59:05 MST.

Mitchell Keil
(mitchellkeil) - F

Locale: Deep in the OC
Re: Re: Re: Re: Marmot Bags and a question for readers on 12/21/2006 18:44:38 MST Print View

Because of the rating method that MB employs, both the #3 and #4 intersect with the WM bag and Marmot bag. The sweet spot temp that MB uses for the 8 hours of uninterupted sleep would suggest the #3 would be the better fit. But much does depend on the sleeper. But you are right that 9oz of down is very close to the amount for each of the other bags. Since I sleep warm, I tend to think of the #4 as my 32 degree bag and it is closer to the actual overall weight of the other two. So perhaps we need a side by side by side by side comparison (or a side to the 4th power comparison.)Regardless, a comparison should be made between MB bags and these other lightweights because of the issues I and others mention in the previous posts.

paul johnson
(pj) - F

Locale: LazyBoy in my Den - miss the forest
Re: Re: Re: Re: Re: Marmot Bags and a question for readers on 12/21/2006 19:01:50 MST Print View

Mitchell, agreed. looks like we are both essentially on the same page. since questions about MB bags come up fr/time-to-time in the Forums, it would be very instructive to see how both a #3 and a #4 stack up to two other primo bags. are the criticisms of 725FP down justified? does the perceived lack of loft and thinness some have mentioned in the past really exist? [note: for my part my WM Highlite has less loft than my MB SSDH #3 by about 0.5".]

Mitchell Keil
(mitchellkeil) - F

Locale: Deep in the OC
Re: Marmot Bags and a question for readers on 12/21/2006 19:37:03 MST Print View

(Just cut down the re: re: on the subject line a bit.) I agree PJ. There are a number of us who own MB bags and the consensus seems to be that most of us are blissed out on them.(Not to mention blissed out on most MB product lines.) So why the constant drumbeat of concerns about 725 fill and inadequate loft and fill for the temp ratings? What I find very interesting is that in a Google search for MB bag reviews, very little has been written except by a few BPL members, me included. I have always felt that they are a great value for the $$ and spot on for temp ratings as well as very well constructed. They deserve to be put up against the best in the bag business -- Marmot, WM, Feathered Friends and the like -- and rated for comparison. So, I hereby request that BPL do a bag comparison to include MB. Any "Aye's" out there?

paul johnson
(pj) - F

Locale: LazyBoy in my Den - miss the forest
Re: Re: Marmot Bags and a question for readers on 12/21/2006 20:35:12 MST Print View

Oh well, i always wanted to be a Pirate, so...

Avast Matey, Aye, i be sailin' wit ya, Arrgh!

Eric Blumensaadt
(Danepacker) - MLife

Locale: Mojave Desert
MY WM ALTERNATIVE TO THE SUMERLITE on 01/22/2007 11:00:41 MST Print View

I considered the Summerlite but got the Megalite instead.
I feel, with its slightly larger girth it would actually be cooler on hot summer nights but also allow for wearing insulated clothing on below 20F nights.
Plus, the Megalite has no side baffles so down can be shifted between the top and bottom to some degree. I've found that, once shifted your body weight keeps it in place.

So...for a few extra ounces I get greater versatility.

Oh yeah, I DID get a Mt'n. Hardwear Phantom 32 bag at REI 1st but returned it when I saw a WM Megalite in the flesh. The Phantom 32 had FAR less loft than the Megalite. The hard part was forking over the extra $100. for the Megalite. Now, after staying warm in the WM bag at 22F, I feel it is money well spent.
The Megalite also has a full length zipper which I feel is a MUST for hot nights.

Edited by Danepacker on 01/22/2007 11:07:42 MST.