What Is It?
Mammut's Cho Oyu is a full-on technical waterproof shell which the company says is ideal for multi-pitch rock climbing, classic alpinism and mixed and ice climbing. Its big selling point is the use of Schoeller's c_change fabric which is claimed to adapt to the temperature and optimise breathability accordingly.
The Techy Bits
Mostly the Cho Oyu is pretty much a standard issue Euro hard shell jacket. Where it differs in in its use of Schoeller's new c_change 3-layer fabric. Schoeller says the structure of the fabric works like a fir cone. When it or you are warm, the structure opens up and allows maximum breathability - the quoted figure of 20,000 g/m2/24h vapour permeability is about the same as eVent.
When it gets cold however, the fabric closes down and reduces breathability keeping more warmth inside the garment. Waterproofness is still a very impressive 20,000mm, so no problem there. Mammut says that between 10C and 20C, moisture vapour transfer rates increase by around 50 per-cent by the way which is a lot.
Other than that, there's nothing particularly radical going on here, bar the perforated chin piece that's reminiscent of a Berghaus design from a few years back and aimed at reducing goggle fogging.
How It Performed
We have to be absolutely fair and say that the Cho Oyu is designed primarily for alpine conditions where temperatures are more varied than in a British spring, so we've found it hard to test the fabric as we'd like to.
What we did find was the in normal use, when the going gets hot, c_change feels roughly equivalent to eVent, though perhaps not quite as breathable in a back-to-back hill-climbing test.
What you're paying the premium for is the bit where the fabric closes down when things get colder with the reduced moisture vapour transfer helping to reduce heat lose. We're willing to believe that this is a significant factor during stop / go work in full alpine conditions, but in non-winter British temperatures, we honestly couldn't tell if the fabric was working or not. If we get to use it in properly alpine climates, we'll report back.
What we can tell you about the fabric is that, at a time when Gore-Tex and eVent seem to be producing lighter, softer-feeling fabrics, the polyamide faced and lined c_change laminate feels thick, tough and a little inflexible. It's also cut very snug, and quite short so you'd best be trim and athletic to match.
Generally the technical features work fine with simple Velcro-fastened cuffs and hem drawcord, though we found the snug cut made the pit-zips hard to open cleanly without snagging under the arms.
The hood is pretty good with a helmet, though a little tight over the OM test chin - try before buying we think - but without a helmet, the minimally stiffened peak offers very little protection and isn't really up to full-on UK conditions in our opinion.
Initial Verdict
It's really early days on the fabric front. On the one hand it does breathe well, on the other it feels slightly stiff and inflexible, if rugged, and we honestly can't detect the changes in breathability across temperatures, possibly because we run hot and the weather has been mostly warm.
In proper alpine conditions, we suspect the difference would be much more marked. Our other query is with the hood. With a helmet it's fine as the helmet lip acts as a reinforced peak, without one though, it's not really protective enough.
So definitely a possibility for proper alpine use, but you're much better off with a more UK-friendly jacket for British hills. And it's very expensive.
Buy if... you're looking for a dedicated alpine jacket with cutting edge technology and you feel the cold once stopped using eVent clothing. Oh, and you're built sleek and rich...
