Mammut Biwak Down Jacket

review of the Mammut Biwak, Blister Gear Review
Mammut Biwak Down Jacket

Mammut Biwak Down Jacket

Size Tested: Small

Reviewer: 5’3”, 120 lbs


  • Durable and water-resistant Pertex® Endurance outer shell, polyamide inner
  • Double-chamber construction to prevent cold spots
  • Insulated with 90/10 goose down with 800-fill power and Fibrefill Body Mapping insets around underams and back to optimize moisture transfer
  • Lycra® hand gaiters
  • Helmet compatible hood with 3-point adjustment toggle system
  • Hide-away hem cinch cord to seal out drafts with sticky gripper tape to prevent the jacket from riding up
  • Double wall insulated outer pockets, 2 inner mesh-lined pockets

Size Small Center Back Length: 28 inches

Blister’s Measured Weight of Size Small With Stuff Sack: 23.1 oz / 651.9 grams

Measured Weight of Size Small Without Stuff Sack: 21.8 oz / 618 grams

MSRP: $500

Locations Tested: Alta Ski Area; Snowbird Ski Resort; Sugarbowl, CA; Steam Mill Yurt, Logan Canyon Utah; Castle Peak Yurt in Uinta Mountain Range, Utah

Days Tested: 50+

Stuffed with a generous amount of 800-fill power down feathers and Fibrefill, the Biwak Jacket from Mammut, a Swiss company, is intended for high alpine adventuring. It’s a jacket designed for climbing, mountaineering, yurting or skiing, and is best used in temperatures below the freezing point. A lean alpine fit and well-designed features make the Mammut Biwak a good choice for those heading into the alpine or the backcountry.

Plus, “Biwak” rhymes with “Ewok,” which is neat.

Fit & Sizing

I am a small in most brands such as Norrona, Patagonia and the North Face, the same holds true for the Mammut Biwak Jacket. Keep in mind that this jacket is designed for alpinism, so the back of the jacket with its drop hem hits quite low, on me it actually hits below the booty. This is one of my favorite features of the jacket, as my buns are warm at all times. This is also great if you happen to be standing around at the crag, sitting down, or marching along mountainsides.

Lexi Dowdall reviews the Mammut Biwak for Blister Gear Review
Lexi Dowdall in the Mammut Biwak, Alta Ski Area.

The front of the jacket also extends well below my waistline, so the overall fit of the jacket is fairly long (significantly more so than my other down jacket, a North Face Super Diez).

The Biwak Down Jacket & the Michelin Man Factor

With a down jacket, there is always the question of how much or how little it’ll make you look like the Michelin Man. I don’t think the Biwak appears overly puffy or shapeless. I receive compliments on the regular when I wear this piece, so with that I assume the fit is somewhat flattering.

Lexi Dowdall reviews the Mammut Biwak Down Jacket, Blister Gear Review
Lexi, Steam Mill Yurt, Logan Canyon, UT. (photo: Jared Hargrave)

It isn’t totally shapeless either, there is some preservation of the feminine form and it features a slightly hourglass shape rather than a barrel.


The worst conditions I’ve encountered in the Biwak would have been pre-season sometime in November touring up at Sugarbowl resort around Tahoe, before the lifts were open for business. Though sunny, the wind was whipping at a miserable 45+ miles per hour, and the temperatures hovered in the teens. I was actually touring uphill wearing this down jacket—comfortably. I felt no wind penetration and the jacket perfectly managed to insulate me in these brutal conditions.

The Biwak features synthetic Fibrefill inserts along the underarms and along the center of the back to help transfer perspiration and speed evaporation of moisture. While I did feel a little damp, it was manageable, and much more so when compared to the times I’ve worked up a sweat in my North Face Diez Down Jacket.

On another occasion, I spent 2+ hours one evening watching an outdoor ski movie in Truckee. The temperature was around 25 degrees and everyone around me was freezing, except me. The Biwak managed to perfectly insulate me in these conditions while standing around for 2 hours, I was thankful to be equipped with such a warm jacket.

Since the Biwak is so warm, I’ve definitely found it to be too much in some situations. I save it for the days in Utah where the temp is 35 degrees F or lower, otherwise this jacket is impractical. I’ve found I actually cannot wear the Biwak comfortably in my car if the heat is on, and heading indoors it’s best to promptly remove it to avoid swamping out. If you inhabit a milder climate, I highly recommend considering alternate options, because this may be overkill. If you live in Alaska, commence rejoicing.

The Biwak is tolerable in milder temps as long as you aren’t engaging in anything that will increase your heart rate. Walking home last night in mild 45 degree weather, I was comfortable in the Biwak. It offers excellent protection in teeth-chattering temperatures, and it can be used in milder temps as long as you keep your heart rate low.

I took the Biwak along on a trip to the Steam Mill backcountry yurt in Logan Canyon, Utah recently, and again to the Castle Peak yurt in the Uinta Mountain Range. For such a large jacket, it does pack down relatively small, enough so that it’s practical to carry into the backcountry. With the included stuff sack, the jacket is approximately the size of a basketball, but it can be stuffed much smaller. A beefy tangelo is about as small as I could squash the Biwak. After climbing up the skin track, the Biwak effectively helped me ward off the chill on the ridgetop as I prepared for the decent. The gaiters helped to keep my hands warm while removing skins and buckling boots and the 2-way main zippers made for easy adjustments to vent if needed. The jacket was awesome for warming up inside the frigid yurt after a long day skiing, the long drop hem and hood helped me warm up rapidly.

Stuff Sack

The Mammut Biwak jacket is equipped with the fanciest stuff sack I’ve ever encountered for a jacket. It is very well-constructed, and features a Pertex bottom with mesh sides. It has a simple elastic closure and a ribbon tab in case you need to attach the sack to another piece of gear.

As I mentioned above, when stuffed, the sack is about the size of a basketball, but the jacket can certainly be compressed smaller. It wasn’t so large that taking it backcountry skiing was a concern.

For quick, ultralight tours, I do choose my tiny North Face Diez down jacket to save space and reduce weight in my pack, but for extended adventures like a hut trip, I appreciated the extra warmth and hood on the Biwak jacket.

4 comments on “Mammut Biwak Down Jacket”

  1. Dear Lexi,

    I absolutely need your feedback about the Mammut Biwak down Jacket in size S.
    I absolutely need a very warm down jacket for my 4 weeks trip in Nepal, while I will be doing 2 summits of 6000.

    I an very skinny, sizing 160 cm for 49 kilos. I would like to know your size to imagine if the SMALL will fit me or too big.
    Because the XS is not existing anymore in my country (Switzerland)

    Thanks for your urgent answer :) Aurélie

  2. Hello Aurélie,

    I am just 2.5cm taller and 5 kilos heavier than you. Though of course the XS would most likely fit you best, I think it would be fine to use the size small. I hope you have a wonderful trip, stay safe up there.

  3. interested to know if you bought the Mammut pants too that go with this jacket. I have the coat and concur on all the things you’ve said!

  4. Hello Darlene,

    I did not buy the pants.
    I only have limited experience with Mammut pants, but what I did find was that the fit is definitely a bit more tailored/alpine. The Euros seem to like a skinnier cut, so keep that in mind when sizing.

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