Mammut Eiger Nordwand IN Flex Air Hooded Softshell Jacket Review
The Mammut Eiger Norwand IN Flex Air is a softshell jacket insulated with a Polartec Alpha lining, featuring a host of technical features that will appeal to winter hikers, climbers, and backcountry skiers. It has dual chest vents for temperature regulation, stretch cuffs, and an adjustable under-the-helmet hood for a front brim. It’s ideal for high-intensity, stop-and-go activities like winter hiking, snowshoeing, and backcountry ski touring, where managing both warmth and sweat is critical. I think it’s the best winter-ready softshell I’ve ever worn, and it’s become my go-to outer layer this winter.
- Core Insulation: Polartec Alpha Polypropylene
- Shell: Pertex Quantum Air 20D
- Arms: Polartec Powerstretch Pro
- Weight: 430g
- Gender: Men’s and Women’s
Warmth and Insulation
The “IN Flex Air” name hints at what makes this jacket stand out. Instead of traditional bulky insulation, it uses Polartec Alpha, a lightweight synthetic lining that traps heat while remaining very breathable. This keeps you warm in cold conditions, but it avoids the swampy, overheated feeling you can get with heavier down or less breathable synthetics.
Mammut uses a slightly different version of Polartec Alpha in this jacket that is made with polypropylene and not polyester, like the Polartec Alpha Direct used in backpacking hoodies. Polartec Alpha Polypropylene is a more technical variant that is warmer by weight and dries much faster, but is less durable. While that makes the jacket even more desirable, it’s the complete product – the insulation plus the softshell outer and features that make this the jacket what it is.
This jacket really hits its stride in active use, such as winter hiking, snowshoeing, or backcountry ski touring, where you’re constantly switching between high effort and brief stops. It’s warm enough to serve as a standalone outer layer in cool, dry weather, but also shines as an insulating midlayer under a shell. It isn’t meant to replace a big expedition parka, but for most high-output winter activities, the warmth-to-weight balance is excellent.
Breathability and Moisture Management
One of the Eiger Nordwand IN Flex Air’s biggest strengths is its breathability. It’s really off the charts. The fabric and insulation are designed to quickly move moisture out. If you’re snowshoeing uphill or hiking hard, you want something that lets sweat escape before it turns into a cold, clammy mess when you stop moving. This jacket handles that transition well.
You can keep it on during intense effort without instantly overheating, which is a big plus in variable mountain weather when you don’t want to stop every fifteen minutes to adjust layers. The trade-off is that it’s not as windproof as a hardshell, but that’s by design: it’s optimized to be a midlayer or a highly breathable outer layer for dry, cool days.
Fit and Mobility
The fit is athletic, but not restrictive. It’s cut to work seamlessly under a climbing harness, with a hem that’s long enough to stay tucked and mesh-backed chest pockets that serve double duty as vents. The sleeves are shaped and articulated for full arm movement, which is important for climbing and technical handling of tools or trekking/skiing poles.
“Flex” in the name isn’t just marketing. The jacket has enough stretch to move with you, which makes a huge difference when you’re doing high steps, reaching above your head, or twisting on mixed routes. The fabric doesn’t feel stiff or crunchy; instead, it’s soft and flexible, which adds comfort on long days.
Hood and Helmet Compatibility
The hood is one of the standout features. It’s helmet-compatible, meaning it can fit over a climbing or ski helmet without pulling the rest of the jacket out of position. Even without a helmet, the hood works well. It has a rear volume adjustment that cinches down enough to stay close to the head, so it doesn’t block your peripheral vision or flap around in gusty conditions. The high collar integrates nicely with the hood, giving good neck protection and helping seal in warmth.
Materials and Durability
As part of the Eiger Extreme line, this jacket is built to take real abuse. The outer fabric is lightweight but more robust than a delicate ultralight puffy. It can handle repeated pack straps, brushing against rock or ice, and regular use on alpine routes. That said, it’s still a technical insulating piece, not a heavy work jacket. You wouldn’t want to thrash it in dense brush or drag it over sharp rock all day, but for typical winter hiking, snowshoeing, and ski touring use, it should hold up very well.
The Polartec Alpha insulation also means it handles moisture better than down and other synthetic fills. If it gets damp from sweat, light snow, or mist, it will still insulate well and dry quickly. That reliability in mixed conditions is a big benefit for winter and alpine use, where the weather can change quickly.
Practical Features
The pocket layout is thoughtfully done. The dual chest pockets are placed high to stay accessible above a harness or hip belt and are mesh-backed, allowing you to vent body heat. The cuffs are snug, but you can easily pull them up your forearms if you need to vent more body heat. The arms are less insulated than the core and made with stretch fleece
Who It’s For
This jacket is ideal if you:
- Spend a lot of time winter hiking, snowshoeing, ice climbing, or ski touring
- Want a breathable, warm, synthetic midlayer that works under a shell
- Need a helmet-compatible hood and harness-friendly
It is not a good choice if you:
- Want a casual, fashion-focused everyday jacket
- Need a super-warm, big parka for standing around in extreme cold
Bottom Line
The Mammut Eiger Nordwand IN Flex Air Hooded Jacket is a serious technical piece for serious conditions. It offers an excellent mix of warmth, breathability, and mobility, with a fit and feature set tailored for winter hikers, climbers, and ski tourers. If your priority is performance in the mountains, this jacket is a strong, well-thought-out option that will become a workhorse layer in your cold-weather kit.
Disclosure: Mammut donated a jacket for review.
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Hi, thanks for the review and pictures! It is kind of hard to find some on such a new item. One thing I really wondered though, and that wasn’t brushed in your article, is the difference between Alpha Direct, used elsewhere in many brands, and the new Alpha Direct Polypropylene used in this jacket. Did you notice they are not the same?
I think they’re exactly the same. Mammut marketing isn’t up to speed on US usage.
No no, Alpha Direct is usually 100% polyester. This one’s lining is 100% polypropylene. I thinks this is worth noting, as these two materials do not have the same characteristics.
Agreed they specifically say polartec alpha polypropylene on the website. Never heard of that before.
I stand corrected. I asked my pet AI. I think there ar eslight differences.
Here is a clear, practical breakdown of the differences between Polartec Alpha Direct (polyester) and Polartec Alpha (polypropylene). They are similar in concept but behave differently in real use.
1. Fiber material
Alpha Direct (polyester)
– Made from polyester fibers
– Fibers are slightly heavier and more robust
– Common in current outdoor apparel (jackets, hoodies, liner layers)
Alpha (polypropylene)
– Made from polypropylene fibers
– Fibers are lighter and more hydrophobic
– Less common and harder to source today
2. Warmth-to-weight
– Polypropylene Alpha- Warmer for the same weight
– Lower density fibers trap more air
– Polyester Alpha Direct- Slightly heavier for the same insulation level
– Still very efficient compared to traditional fleece
Summary: polypropylene wins on pure warmth-to-weight.
3. Moisture behavior
Polyester Alpha Direct
– Absorbs a small amount of moisture
– Dries fast, but not instantly
– Can feel damp during long, sweaty efforts
Polypropylene Alpha
– Practically zero moisture absorption
– Moves sweat away immediately
– Dries extremely fast
Summary: polypropylene is better for high-output activities and humid or cold-wet conditions.
4. Durability and longevity
Polyester Alpha Direct
– Better abrasion resistance
– Holds structure longer
– Easier to sew and more tolerant of repeated washing
Polypropylene Alpha
– Fibers are more fragile
– Can flatten or break down faster
– More prone to fuzzing and damage
Summary: polyester lasts longer in daily use.
5. Softness and next-to-skin feel
Polyester
– Slightly softer
– Feels more like fuzzy fleece
– Comfortable against bare skin
Polypropylene
– Feels drier and more technical
– Slightly scratchier
– Often better with a base layer underneath
6. Odor resistance
– Polypropylene Alpha- Better natural odor resistance
– Polyester Alpha Direct- Can retain odors more easily unless treated
7. Temperature stability
Polyester
– Better heat resistance
– Safer in dryers and in warm conditions
Polypropylene
– Lower melting point
– Needs gentler care
8. Availability and use cases
Polyester Alpha Direct (common)
– Widely available
– Used by brands like:- Senchi Designs
– Rab
– Arc’teryx
– Outdoor Research
– Best for:- Versatile active insulation
– Everyday outdoor use
– Frequent washing
Polypropylene Alpha (rare)
– Mostly seen in:- Military and niche technical projects
– Best for:- Ultra-light systems
s
– High-exertion use
– Cold, wet environments
Bottom line
– Choose polyester Alpha Direct if you want:
– Better durability
– Softer feel
– Easier care
– Broad clothing options
– Choose polypropylene Alpha if you want:
– Maximum warmth per gram
– Fastest drying
– Best performance when sweating hard
I have a similar jacket by Rab. It’s my favorite jacket, you can hike all day in it with just a base layer and never have to change. The only negative is that it’s bulky in a pack.
I just never take this off in winter. If I’m cold I layer over it with a polarguard vest or a hard shell.
Very interesting piece of Kit for sure.
Most of the gains in warmth, lightness and low bulk have come from the smaller cottage industries. Finally the big names are starting to catch on.
Up until this point I haven’t found anything that dumps heat effectively during high exertion. I’ve tried my Cashmere sweater , Patagonia Ri Air Hoody, Rei Expedition thermal top, and Vario jacket . All kept me super warm but were way too hot to hike or backpack in.
I always use the Brnje mesh top as my first base layer and that works terrific but have yet to try my Zpaks Octa fleece top over it.
I’ve saved my Octa fleece for sleeping duties but maybe it might work for hiking and backpacking
So here is the next test:
1) Brynje mesh top.
2) Zpaks Octa Fleece hoody
3Copperfield windshirt
4) Add on of a Eddie Bauer thin down vest if colder.
5) And Mont Bel down sweater if brutally cold.
Small clarification – polartec alpha was in use well before the cottages started making hoodies out of it. They’re only “innovation” was to decouple it from an outer jacket and sell it standalone.
After thinking long and hard about how this top would work in my Kit I finally broke down and purchased one .
Mostly based on your review Philip which is one of only a couple I could find out there on the Interweb. Thank you for that in depth review and suggestion.
I must admit after 50 plus years of climbing and hiking I never had a true Softshell that performs like this one. I always used the layering system and then topped off by some wind or waterproof outer depending on conditions.
What I found was I had to choose between keeping my core warm and arms cold or both arms and core too hot.
My criteria was simple- find a highly breathable softshell that is lightweight and dumped heat like no other . It also had to stand up to the abuse from the Krumholz frequently found in the Whites and Adirondaks.
But first I had to get over that Stratospheric price tag. At 400 bucks its a decision one doesn’t take lightly and easily outpaces anything else out there from the top names in the industry. Lucky for me I found a 20% off sale on Backcountry.com and pulled the trigger.
By the way the closest I could come to the performance of this one was the Patagonia R2 Hoody.
Since I just purchased the Mammut recently ( 1-26) I’ ll share what I know and then update later if you don’t mind.
The first thing that strikes me is how light this garment is from its claimed weight of 15oz. Using my Lie -O-meter scale it came in at a svelte 13oz. Impressive for such a feature packed garment. It also is much less bulky and packs up way smaller than my Patagonia R1.
The second thing that impressed me was its quality construction. All the stitching seems well done and looks like it might last a long time . Hope so at this price point.
The third item is the fact that in the upper part of the arms there is a slippery Polyester fabric so its easier to get on and off as opposed to all fleece going all the way down . This casing is sewn OVER the Polypropylene Alpha Direct . Said differently the Polypro goes all the way down the TOP of the arms. Underneath the forearm is brushed fleece.
Fourth holding the garment up to the light you can see right thru it. This would indicate high breathability. Combined with Pertex Air outer shell it still should be wind resistant.
Fifth is the front part of the garment goes up up past the chin and falls right under my nose when fully zipped . I’ve never had one that comes up so high and stays there. A welcome feature on those brutal high wind summit climbs.
In my testing at 9 degrees F I wore my Brynje mesh base followed by a Patagonia super thin zip T neck and then the Mammut Eiger . Over that I wore my Outdoor Vitals NovaPro vest similar to what you did in the picture.
I was hiking so that would be considered moderate exertion and I felt very comfortable with just enough warmth. Not too much not too little . Much better that any combination I could muster previous.
I’ve got a Pulk sled deeps woods camp planned and that will test a higher level of exertion.
More testing needed…
Hope this helps someone.
Yup. It’s exceptional. Mammoth stuff is awesome