The construction of the Bison DL is immaculate. I am right-handed, so i got a left-zip, and it works great. No zipper binding, all the velcro fit and held tight, the cord locks were easy to get to and operate. The size is intimidating, and the bright red color subconsciously makes you feel warmer just looking at it. At 6'1 and 170 lbs, I got the long (6'6") version.
The footbox is just great. There is plenty of foot room, which is something I was initially worried about. Tons of room to store next morning's clothing or other items that you don't want freezing without interfering with a good night's sleep. The bag is just about the right fit, and has plenty of wiggle room inside. It is far less constrictive than I initially feared. If you like to sleep curled up on your side, its no problem, the bag moves with you.

My first test of this bag was on my porch on a single-digits F night. I jumped in and cinched all the fittings up tight so only my nose & mouth poked out. The bag went from freezing cold to comfortably warm in about two minutes.

I woke up sometime in the middle of the night sweating to death. It had gotten so hot in the bag that I was unconsciously triggered awake, and I was roasting. I unzipped everything and aired it out quickly, then left it mostly open for the rest of the night (uncinched the hood, etc.). It worked great after that, perfectly comfortable, like sleeping in a warm house.

I am a cold sleeper in general, so most bags feel less warm to me than they are rated for. This one has worked great for me for any sub-freezing temps so far. I do not know the upper limit of its range yet, the warmest I've used it in was high 20's F weather. Leaving it unzipped will definitely be necessary in warmer weather.

I had one problem, when leaving the hood open my face got extremely cold exposed to the open air. The solution: throw a fleece over your head. My Black Diamond fleece was just perfect for keeping most of the bitingly cold air off and a little warmth in, but still breathable enough that I didn't hardly notice it.

I have also used this bag zipped open as a topside blanket in conjunction with another rectangular bag on bottom. It worked great for two people huddled under it in teens weather at night.

The only other drawback to this bag is also one of its benefits. It's so big. Not even so much in weight, especially considering how it performs, but just in pure size. It packs up pretty tight into its stuff sack, but its still way too big to put inside the sleeping compartment of my Kelty Red Cloud pack. Throw it in a good OR stuff sack and it should ride out any weather strapped to the outside of a pack. After all, it is shelled in DryLoft.

Oh yes, the last thing to consider, price. If you can pay to play, this bag will do you no wrong, but at $710 MSRP its sure to be one of the most expensive things in your collection. On the other hand, for a bag that works, from an excellent manufacturer, that will last probably 20+ years, and can save your bacon if the $%#* hits the fan...

Similar Products Used:

None

WM Bison SDL is a superb sleepingbag! The materials and the craftsmanship is of highest quality, and the design is perfect for cold weather use. I used the bag on Denali this year and I wasn't cold even once, although the temperature dropped to -38 Celsius (-36 F) one night. In fact I was too warm a few nights when the temperature stayed between -30 and -35 Celsius (-22 / -31 F). The conditions were mostly cold and dry so the DryLoft shell wasn't really tested, but it worked fine in those conditions.

My two climbing partners had Marmot Cwm and ME Everest, both rated to -40. Those are also fine bags, and my friends were not cold in their bags. However, my WM-bag has in my opinion a better design, and is also slightly thicker without being heavier.

The only thing that I'm not satisfied with is the velcro closure of the collar. The 2000 bags has a different solution compared to my other WM-bag from 1998, and I think the old one was better.

Similar Products Used:

Caravan Arctic Isblå (Swedish), WM Big Horn Super MF