I use this bag for winter mountaineering and mid winter ski trips where I will be sleeping in a tent. I LOVE it.

The bag has a COMFORT rating of -20f (-29c). Some reviews out there have mentioned the extreme rating (more of a survivability rating) at -40c.

The 800 fill down is excellent and very light, and the 15 denier by 15 denier ballistic ripstop DWR treated nylon is lightweight and surprisingly strong. It will bead water like the best DWR treatments- if you spill a water bottle on it, the water will roll off. However, long term condensation or prolonged exposure to standing liquid can cause the nylon to absorb some water.

The most unique feature of the bag is the stretch design. This does two things.
1- it allows the user to comfortably move inside the bag. Because there is extra room, one can wear extra layers without having to worry about the "push out" effect that can cause most conventional mummy bags to compress their down and cause the bag to not be as warm.

2- The stretch design conforms the bag to the user's body, eliminating dead air space and keeping the user warmer. With less air space to heat up, your body doesn't have to metabolize as much energy to keep you warm.

This bag is surely one of the best on the market. The only change I would suggest is an option for a dryloft bag with a membrane water proofing for additional protection in moist environments.

Note the sizing differs from most companies- the regular is only a 5'10'' bag and the long is only a 6'4 inch bag. I'm 5'11'' and find the long perfect in that I can fit my boots and cloths I want to keep warm in the bottom of the bag with me.

Also note that opposing zipper Montbell Bags can zip into each other- (left into right) for all bags both synthetic and down and regardless of length. My girlfriend and I zip a MB UL SS #2 into this bag and orient the bags put the EXP on top (instead of side by side) for winter couple camping.

One last thing- besides the added room for storage, the long is a great option for shorter people because foot box area of the bag can fold in on itself and cinch down inside the bag, allowing for either a down pillow for your feet or an extra super thick layer of down on top of your feet to keep you extra warm. To do this, just push the footbox into the bag and pull the draw string about 6 inches from the bottom of the bag.

After having these for several years they have proved to be great crampons for more technical use. They are solid performers all around. Unlike old "vertical rail" super rigid crampons that people climbed vertical ice with, these are much more versatile. The design allows for a little bit of flex which makes walking significantly easier and much more natural when you aren't on super steep terrain. The flex is a non issue for climbing though, as boots with a toe bail will have a stiff enough shank to support front pointing.

The attachment system is nice and secure as well. Replaceable front points offer added value over other brands. When you wear out your front points, replace them without buying a whole new set of crampons.

While they aren't ideal for glacier travel, they are great if you will be crossing a glacier on approach to an alpine climb. All in all, SOLID!

I love these boots. Great fit, extremely comfortable, and warm enough for the winter ice climbing and mountaineering that I use these for. It is important to note that these are significantly warmer than the older version from several years ago, which did not have a Duratherm lining.