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CWM Sleeping Bag: -40F Down

5 out of 5 stars
10 Reviews

Style & Size:


Why We Like The CWM Sleeping Bag

We like to get some shut-eye in the death zone with a little help from the Marmot CWM -40 Degree Down Sleeping Bag. This 800-fill goose-down-insulated bag is built for the coldest, harshest weather on the planet, from the South Col to the South Pole. Its waterproof, breathable Pertex Shield 2L laminate prevents rogue bits of water, tent condensation, and melted snow from clumping your down and ruining your sleep (and chances of summiting tomorrow). The outer fabric itself is made from rugged 30D nylon ripstop and the lining from 30D nylon ripstop Pertex Microlight, which has a soft feel and the durability to prevent feather leaks.


  • One of Marmot's warmest sleeping bags built for mountaineering
  • Waterproof, breathable Pertex Shield 2L maximizes weather protection
  • 800-fill down insulation has a temperature rating of -40F
  • Cross-baffle construction and draft tubes prevent cold spots
  • Adjustable hood cinches tight for the coldest nights
  • Storage and stuff sacks included
  • Item #MARZ9N1
[membrane/laminate] Pertex Shield (2-layer), [face fabric] 30D nylon, [lining] Pertex Microlight (30D nylon)
800+-fill Power Goose down
left, right
Max User Height
[regular] 72in, [long] 78in
Shoulder Circumference
[regular] 63in, [long] 65in
Hip Circumference
[regular] 61in, [long] 63in
Foot Circumference
[regular] 44in, [long] 46in
Bag Length
[regular] 83.5in, [long] 89in
Draft Tube
Pad Retainer
Fill Weight
[regular] 47oz, [long] 50oz
Storage Sack
Stuff Sack
Stuff Size
9.5 x 19in
Claimed Weight
[regular] 4lb 15.5oz, [long] 5lb 4.5oz
winter camping, weekend camping
Manufacturer Warranty

Overall Rating

5 based on 10 ratings

Review Summary

1 Stars - 0 reviews
2 Stars - 0 reviews
3 Stars - 0 reviews
4 Stars - 0 reviews
5 Stars - 10 reviews

Fits Small

Screen reader users: the following list provides a visual scale to illustrate the product fit. Please refer to the heading above for the fit type in text.
Runs smallTrue to sizeRuns large

What do you think about this product?


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5 out of 5 stars

January 22, 2024

Nice bag, long enough, on sale, good deal

[This review was collected as part of a promotion.] Nice bag, long enough, on sale, good deal, bought two of them, zipper doesn't get stuck, recommended

Cool dude

Originally reviewed on

5 out of 5 stars

January 14, 2024

Ridiculously warm

Finally got a chance to field test the bag in zero degree conditions. Once inside, I never noticed the chill. I even shedded a layer half way through the night. The col is by far the warmest sleeping bag I've ever tested.


Originally reviewed on

5 out of 5 stars

December 16, 2023

Just do it

WARM! Big, but definitely warm. Love that the zipper is in the center. Also love the pockets inside the sleeping bag.

Kelly B17

Originally reviewed on

5 out of 5 stars

October 6, 2023

Really nice bag; runs small

Size Bought:
5' 11"

It's warm; I like the central zipper. Some folks have written reviews saying the zipper is hard to use -- maybe they updated it? Quite the large/easy zipper to me. And small zippers drive me nuts! I'm writing this to note that as someone 5'11, I don't think I'm a regular, even at that is rated to 6 feet. My toes touch the bottom pretty firmly. If I were say 5' 9, I'd be quite happy. And this is me in the bag in my pajamas, not some climbing snowsuit. I'm surprised this is the case....

Bruce J
5 out of 5 stars

July 8, 2023

Dream Level Comfort

[This review was collected as part of a promotion.] I have a collection of sleeping bags that I have acquired over many years of backcountry travel and recreation. All are down, and all come from reputable, high-end outdoor companies. They are all nice in their own regard, but I can honestly say that none come close to this beautiful sleeping bag. From the superb warmth of the mega-stuffed down filling, to the cleaver zipper layout, this bag delivers dream level comfort. I have yet to test it to it's -40 degree rating, but it has over performed snow camping and skiing the Eastern Sierra's. Not a hard choice picking this bag, however, I did dither between the -40 degree and the -20 degree option. It would have been plenty warm and I like the yellow color, but I figured, "go big", after all I am the Original Marmot Man.

The Original Marmot Man

Originally reviewed on

5 out of 5 stars

December 26, 2022

Like being in Heaven. You won’t regret buying this

[This review was collected as part of a promotion.] I FINALLY HAVE ONE! I’ve wanted a Marmot bag for over 30 years and it’s worth every penny. Marmot has used their years of experience perfecting this sleeping bag. I love the features and boot bag and extra foot room. I am 6 foot and got the 6’6” bag- zippers don’t snag with their technology. Side zips are great. You will love this bag. I used mine with double groundsheets and recommend 1 for insulation - while I was not in a tent.

MattW Michigan

Originally reviewed on

5 out of 5 stars

December 14, 2022

Absolutely worth it!

I was hesitant to buy with the price tag but I live out in the middle of nowhere oregon up in the mountains at 5000ft and go to around 8000 all the time for winter camping, this thing had been amazing!


Originally reviewed on

5 out of 5 stars

December 14, 2022

800 fill sleeping bag

[This review was collected as part of a promotion.] Best...warmest bag I have ever used!! Never cold!!!


Originally reviewed on

5 out of 5 stars

November 25, 2022


[This review was collected as part of a promotion.] I live in Alaska and I backpack all year round and I have an unheated tent in the Winter. The previous CWM was awesome but this bag is 5 plus. I love the central zipper, I love the inside pocket to put my cell phone and headlamp in so they do not die from frozen batteries. I love the gills that not only limit condensation without losing critical warmth.I love the way it lofts up, it, like its predecesser, is a giant marshmallow. I took it to a fundraising sleep out (in the snow) last week. It was about 2F so this was plenty warm without a shelter. I am a short guy but I buy a long bag,as I put my boots in a trashbag inside the footbox at bedtime, so I do not put on frozen boots in the a.m. When its really cold, you can ruin a good time with frostbite,


Originally reviewed on

5 out of 5 stars

June 10, 2022

Super warm bag and it compress down small!

[This review was collected as part of a promotion.] I just got the new CWM -40 bag right before my trip to climb Denali. I get cold easily when the Temps fall below zero so I wanted to make sure I had a warm bag. On Denali at 14,000 feet and above the Temps ranged from 0 to -15 degrees from 7pm to 8am. I spent 11 nights on the mountain and I only zipped up the bag 1 of 11 nights. I was toasty warm the whole time. I was also very please how much I could compress the bag to fit into my pack. I highly recommend this bag if you get cold of night or need a super cold weather bag.


Originally reviewed on