The Sub Zero is extremely warm. It is by the far the warmest jacket in this review and is ideal for cold, snowy, and wet conditions. Mountain HardWear's Conduit SL material is very water resistant (but not water proof because of the lack of taped seams), which makes it a good jacket for mountaineering pursuits where you could be getting wet as well as cold. Like the Nuptse jacket, there are reinforced patches on the shoulders for added durability when wearing a pack.
The Sub Zero has many interesting and useful features. The fit of this jacket is longer than all the other jackets in this review, which is nice because it protects more of your body from the elements. There is a drawcord inside the jacket around waist level that can be pulled tight to keep wind out and seal in even more warmth around your core. There are Velcro closures around the wrist cuffs for the same reason. There is also an interior water bottle pocket, which is a handy feature for mountaineering when your water is likely to freeze.
In our Outdoor Gear Lab hose testing we determined that the Mountain Hardwear Sub Zero was one of the most weather resistant down jackets in our review. While no down jacket is great in the rain, the Sub Zero was about as good as it could get and repelled wet snow and a light drizzle better than we could have asked for. The hood is copious and fit all helmets we tested. We liked the face covering flap a nice addition that protected most of our face even on the windiest of days. The Sub Zero is also one of the few baffled jackets we tested, a design that adds quite a bit of expense but greatly increases the warmth of the garment.
The same features that make it one of the warmest and most water resistant parkas in our review also make it one of the bulkiest and heaviest. Part of this is the heavy Conduit shell, which is exceptionally water resistant but heavy. It was the heaviest jacket reviewed, weighing in at 1 lb 10 oz. (an entire pound heavier than the Mountain Hardwear Nitrous Jacket), and it is the only down jacket in this review that does not stuff down either into a pocket or a stuff sack. However, these complaints come with the tradeoff of the Sub Zero being ridiculously warm. If you are looking for a jacket for extreme conditions, the weight and packability hardly matters. The Sub Zero does have a lower quality down than most of the other jackets, using 650 fill down rather than 800 fill down like the Patagonia Down Sweater, the MontBell Alpine Light Parka, and The North Face Catalyst jackets. This lower quality down is partly what makes the jacket so bulky and heavy — if it was made with 800 fill down it would most likely be lighter but also far more expensive.
I am not sold on the detachable hood. If it is necessary to wear a jacket that is this warm, a hood would be wanted as well, and it doesn't seem to add much functionality by being able to take it on and off. The zippered seam where it detaches is just another spot where wind can leak into the jacket. The Velcro closure in the front of the hood is nice because it closes in front of your face to keep your chin warm, however a gap is left under the Velcro and wind comes right in. It would be warmer and more functional if is actually sealed closed in some way in front of your face. If you want to save a bit of weight and do not like having a hood, this jacket is also sold as a non-hooded option.
The fleece-lined hand warmers are nice for wearing around town but add weight for applications where you want to move light.
As one of the warmest jackets we tested, it is a great option for cold weather camping, mountaineering, ice climbing, and skiing. A little too warm for summer camping.
This jacket isn't cheap. However, you are paying for a thick and warm jacket with a water resistant fabric. The non-hooded version of this jacket is not made with the Conduit SL material and is significantly less expensive — $185 — which is even cheaper than The North Face Nuptse.