Mountain Equipment's lightest ever waterproof shell jacket, the Impellor would be well suited to any weight conscious activity, from hill running and ultralight walking to minimalist mountaineering. I used it hill running and Nordic skiing throughout the winter, and since then it's enjoyed plenty of miserable damp hill walking and scrambling. More recently, I've carried it in the hills but not needed to use it thanks to the hot dry weather - and here its lightweight packability has of course been very welcome.

I was out and about having snowy adventures during the 'Beast from the East' Met Office red weather warnings, and on the whole I never felt under-dressed for the conditions despite the lightweight nature of this jacket. The Impellor has the look and feel of a mountain waterproof and yet the weight of a running shell – does this mean it can do a bit of everything? Within limits, yes I guess so.

Fit & Cut

I've been reviewing a size medium jacket. I'm about 5'11'' and 75kg, and this is well sized for me. The fit and general design of the jacket gives the sense you are wearing a mountain type shell rather than a minimalist running cagoule. However the fit still feels close and 'active' – there is not much room for too many mid layers under there! While the Impellor would be suitable for a number of intended uses in the outdoors, in winter it's arguably better for more aerobic heat-generating activities, things like running and skiing where you're not going to want too much insulation under your shell.

There is however one irritation which is potentially problematic depending on the intended usage – the cuffs. These are quite close fitting and have only a short (6.5 cm) elastic section. This means that at full stretch the circumference of the cuff only increases by a relatively marginal amount, from ~21cm to 24cm in the case of size Medium (that's only around 14%). I use a Suunto GPS watch for running and most other mountain activities; I found it quite difficult to get the cuff over this, and I have given up trying. In addition if you are using even relatively thin gloves you seem to have a battle on your hands to get them tucked in once they are out. So, using the jacket at times where gloves are essential may create a weatherproofing nuisance; this is a shame given the credentials of the fabric used for the Impellor.

The hem is not adjustable, instead having only very short stretchy sections of similar nature to the cuffs; I feel these are far too small to have any useful role, and a full elasticated hem would be better. On the other hand if you did have a drawcord in the hem then this might ride up when tightened, something that especially seems to happen to me in lightweight shells. Thanks to its decent active cut the lower edge of the Impellor jacket does tend to stay put in most conditions, even when your arms are raised, and because of the close fit of the jacket it does not flap about in the wind.

People commonly wear a waterproof jacket in wet weather without using over-trousers; for example during hill running. In these situations it would be great if jackets were just a little longer, even if only a few cm. This would permit a chaff-free, drier groin area, and would make hill life so much more comfortable. Though Mountain Equipment do often go for a longer-than-average hem in their shells, the Impellor is unfortunately on the shorter side.

Incidentally if you wanted to get a full set of waterproofs there are no obviously corresponding shell trousers in this same range. This may be important to those interested in using this for hill running because of course full waterproof body cover is mandatory kit to carry in all UK races.

I used this jacket on a miserable couple of Cuillin ridge days in early June. It was comfortable to wear over just a baselayer when working hard, but still had room enough for a fleece hoody when the wind inevitably got up. It felt neat, allowed me full freedom of movement when scrambling, and kept all the rain out. It's ideal for a Cuillin traverse, being near weightless when carried but sufficiently weather proof if the crap hits the fan (at which point you may well be heading down anyway).

Fabric

Weighing just 169g in size Medium, the Impellor jacket is constructed from 3-layer GORE-TEX® Active 2.0 throughout. Although very thin, the 3-ply nature of the fabric means it feels pretty tough. However it has a noisy 'rustle' when in use, which might be particularly annoying when running. Secondly the fabric has a very modest amount of stretch; this helps achieve unrestricted movement despite the close athletic cut of the jacket. Exceptional breathability is a key selling point of this fabric and so its use seems logical for a jacket intended for high-energy outdoor pursuits. In my experience it works well. Remember though, however breathable a fabric claims to be you will still get sweaty depending on your rate of energy expenditure and the environmental conditions in which you are exercising.

The fabric in this case is great, but why do Gore-Tex only provide it in a dull graphite grey? You're only going to wear a waterproof shell on the gloomy wet days; will no one think of the photographer?

Hood

There is a volume adjuster at the back of the hood, but not at the front. However moving the main front zip up and down is a fairly sensitive way of closing or loosening the hood. At least for my sized head, there is no chance of it blowing off when zipped fully up. It is definitely not helmet compatible in the usual sense of the word – however, being unstructured, it does fit absolutely fine underneath a helmet.

Other features

Simplicity is one of the Impellor's key selling points. There is one external pocket, just big enough for my smart phone or a cereal bar. The inner wall of the pocket is perforated with a number of holes and hence this can act as ventilation. For example when I was running with the pocket open it helped keep my torso cooler on a blowy day with the jacket zipped up. Don't try this if you have any valuables in there!

The YKK zips on the front and pocket are water resistant. Oddly, only the pocket zip has a cord extender – I've found this makes finding the front zip more awkward when wearing gloves, especially when it is zipped right up beneath the chin.

Summary

At £200 it ain't cheap, but what you get for the money is a highly breathable multi-use waterproof jacket that will be a hit with hill runners, ultralight walkers and minimalist mountaineers alike. There is a lot to like about the Impellor, but with a few tweaks it could be really excellent. In particular I think the narrow cuff design is a bit of an oversight, as these are pared down to the point where their function is compromised. To be fair, inadequate cuff size on shell clothing seems to be a common moan among glove-wearing mountain types, but if you never intend to wear the Impellor with gloves or a bulky watch then the cuffs may never be a concern. At only 169g (size M), its lightness is the Impellor's key feature, and pretty impressive it is too. For most occasions outside of full-on winter walking and climbing, this could be all the shell you need, and it comes at a weight that you'll barely notice in your pack.