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Forty below zero is a magical place where Fahrenheit and Celsius intersect, as well as an incomprehensible icy hell that can suck the life force right out of you. Come prepared to do battle with the epic cold thanks to the Western Mountaineering Bison Gore WS Sleeping Bag. An extremely weather-resistant Gore WindStopper shell and a whopping forty two ounces of premium 850-fill goose down let you hunker down when the temperature plummets to ungodly lows, and you can trust in the V-Block side baffles, double interlocking draft tubes, and insulated hood and collar to seal out the chill in the big mountains. When the difference between life and death comes down to your sleeping bag, the Bison doesn???t compromise.

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Here's what others have to say...


They Just Don't Make Them Better

  • Familiarity:I've used it several times

I own a variety of Western Mountaineering Sleeping Bags and Garments. I finally has the nerve to fork up the money for this baby. I recently just took it to Mt. Shasta when is plunged 20 below zero(-20). I was cold at first but about 10 minutes later I was very warm. About 30 minutes after I was about to sweat due to the heat this baby retains. This was an easy fix by opening up the bottom zipper about 3 inches to let some air circulate. After that I was fine. This was built extremely well and fits most body types perfectly. I actually had it special ordered because the winter season bags was over so I had the privilege of picking it up at the factory in San Jose, CA. Truly all hand made. It took 2 woman two full days to finish it. Your money is going straight back to our economy and much pride is developed when you get your hands on it. Let me know if you have any more questions.


If you want to stay warm...

  • Gender:Male
  • Familiarity:I've used it once or twice and have initial impressions

This is the warmest and also best constructed sleeping bag I have ever seen or used. Zippers work! Bit heavy as you're going to have with a quality -40 bag, but obviously built to perform and last a good while. Very happy with the bag and surprised how well it can pack if you really take your time. Have not tested the temp rating fully, but at 0 can be almost fully unzipped and still warm.


Simply the best

    Western Mountaineering makes sleeping bags, and not much else. THIS is what they do – they make the world's best sleeping bags.

    If you want the absolute warmest bag on the planet, THIS is the bag to buy. Other manufacturers make "-40" bags, but no one packs as much down into their bags as Western Mountaineering. They cost a bit more, but you're paying for more down. More down = warmer bag.

    A great bag to be sure, but not quite up to Feathered Friends Snowy Owl

    TOTALLY AGREE with oldguy68, you are absolutely CORRECT!!! ...Feathered Friends Snowy Owl is much better, in both packability and performance. The Bison is definitely NOT packable due to the Gortex material used on its system. I am also loving VALANDRE Thor, by the way. I am wondering if there is a Skandinavian bag out there that would out perform the Snowy Owl, the Swedish manufacturer has been known to have a very smart design and quality.

    Unfortunately, as Feathered Friends makes exceptional bags, they do not compare because the GWS(Gore Wind Stopper) used in a the Western Mountaineering bag is so you can use them with out a tent is windy conditions if needed in emergencies or outdoor recreation as most people posted pictures of already. The Snow Owl uses a "Pertex� Shield EX waterproof/breathable" which is much thinner less durable which is obviously less ideal in outdoor conditions. As far as the packability goes, turn any Western Mountaineering bag inside out and you can compress it twice as easier. I am easily able to get the Bison in a Large(20L )Sea-To-Summit compression sack and compress it to about 12L. Bottom line, if you want a bag that is fragile and heavier by over 16oz, get stick with Feathered Friends, if you are looking for a more durable, longer last bag, stick with Western Mountaineering. As far as the warmth goes, -60 degrees is way over rated for the Snowy Owl. It is warm, but not as warm as the Bison. If you want the Bison even warmer, ask for the over fill option and they put even more down bringing it to a true -50 degrees.

    Is this bag water resistant?

    Is this bag water resistant?

    Yes, it uses Gore WindStopper which is incredibly water resistent, and close to water proof, but not seem taped.

    Best Answer

    Gore WindStopper is not waterproof. It is water resistant, but I wouldn't stretch and say it's incredibly water resistant. Basically, it'll be a little better than your typical DWR coated nylon bags.

    When comparing the WM bison and the Marmot...

    When comparing the WM bison and the Marmot CWM, it seems both are great bags, similar weight, quality, etc. However, is there anyone who has compared them for shoulder, hip, foot girth, other than the numbers supplied by the companies? Roominess for a big guy in the long sleeping bag would decide for me which is more suitable.

    This is a roomy bag. Seriously. 64" gives you enough space without feeling confined and not too much space so that you are wasting your heat trying to warm an oversized bag. I don't know about the Marmot bag dimensions, but you'll be very happy in the Bison!

    Best Answer

    I have the Bison and my girlfriend has the Marmot. Both are great bags, but if we were to pick one ?�it would be the Bison. One nice thing: The two brands have mating zippers. woooo!

    The Marmot CWM -40 is extremely packable, but the -40 rating is highly pimped out, IMHO. I was able to stuff it into a 31ltr compression bag without any struggle, but it is not warm enough for Denali-- for sure. I was disappointed with The BISON because it is crazy huge and stiff as hell...but it's got its own fan base, if you try to badmouth the Bison on here, I'm sure they'd bite your head off ! LOL


    Never cold!

      Sorry, I did not buy it here but... This thing is amazing. 13 days on Aconcagua...never could zip it up. And summit day was bone chilling cold with can't stand up kinda wind. It lofts so much it fills a tent..but hey, whatdya want. The only complaint is the bulk. Really hard to zip into the base of a large backpack. But the point of this bag is to keep you alive and comfortable. If it doesn't do that nothing will. Lots of money but never regretted it.

      Never cold!

      Hi Pummel, what kind of compression bag do you use for the Bison? (*and what size?). Many thanks in advance.

      What is the quality difference between the...

      What is the quality difference between the Marmot CQM, and Western Mountaineering Bison Gore, other than the Gore material and price?

      Best Answer

      Western Mountaineering uses 850 down fill while Marmot uses 800 fill. WM is also made in the USA where as Marmot is made in China. Wm is also lighter than Marmot. IMHO I would not spend the extra money on the WM bison over the Marmot CWM because they are both rated for -40 and both have a lifetime warranty. Marmot started out as a sleeping bag company aswell and they also have some of the cleanest down available! As far as quality goes they are both great bags and there really is not much difference.

      All of Marmots high end down bags are filled and finished in Santa Rosa, CA

      How thick is the loft of this sleeping...

      How thick is the loft of this sleeping bag?

      10 inches of loft on this bad boy to keep you nice and toasty.