Mountain Equipment Aeon Jacket

Lightweight packable rain jacket. Good for the occasional shower but not so good in prolonged rain because of limited breathability.

The Mountain Equipment Aeon is a light rainjacket. It has an adjustable peaked hood, elevated side pockets, a small chest pocket, and underarm ventilation zips (pit zips).

The hood is adjustable in the normal way with two pull cords in front and one at the back. The front cords come out below the collar so the wind can’t whip the ends into your face. The only downside of this arrangement is that I have found myself pulling the left cord by mistake when I meant to open the chest pocket.

The hood folds into the collar so that it doesn’t flap about if you are wearing the jacket for protection against wind.

The jacket packs away quite compactly in its own stuffsack. In practice I don’t use the stuffsack to avoid shortening the life of the jacket by scrunching it up tight. Modern rainjackets are usually made of a waterproof membrane bonded to an outer face fabric and, apparently, tightly folding such material can eventually cause it to delaminate. Space in my rucksack is not that limited, so I can afford to roll the jacket up loosely into its hood.

The jacket is made from Mountain Equipment’s own proprietary Drilite material. This has a 20,000mm hydrostatic head and a breathability rating of 20,000g per square meter per 24 hours. The breathability rating is not as good as that of Gore-tex but still respectable—on paper at any rate. Official specifications are one thing, performance in the field another.

The outer face fabric of the jacket is 40 denier, while the inside has a pigment print finish to make the material feel comfortable on the skin. The print finish is used instead of an inner layer to reduce bulk and weight. Jackets with an inner layer are known as 3-layer jackets (the waterproof membrane being the middle layer) while jackets like the Aeon with an inner print finish are known as 2.5 layer jackets.

The Aeon is lightweight—my size medium weighs 343g or 12oz—but durable. During a recent eight-day trek in Scotland I wore my jacket under a large rucksack. The material coped well and I saw no deterioration from friction with the rucksack or its straps.

The jacket is cut to what Mountain Equipment calls an alpine fit. It has nice long sleeves so your wrists stay covered up in the rain, but the body has a slim fit and there is little in the way of excess material for the wind to catch hold of.

The downside is that there’s a limit to what you can wear under this jacket. I am 6' 1" with a 41-inch chest. My size medium fits comfortably on top of a base layer, shirt and fleece. I have also worn it over a light insulated jacket, but this is a tight fit and the Aeon won’t accommodate anything thicker underneath.

The cuffs of the Aeon can be tightened around your wrists in the normal manner with velcro strips. Those on the Aeon are narrower than usual and the jacket has come in for some criticism because of this, but I have not found it to be a problem in practice.

Elevated side pocket

The Aeon has elevated side pockets which just about clear the hipbelt on my rucksack. Each side pocket is big enough for a map, though getting a map in and out is awkward because the zipped opening of each pocket is rather short. There is also a smaller chest pocket which I find convenient as a place to keep my mobile phone, even if the phone is liable to get wet from condensation in the rain.

The most important aspect of a rain jacket is, of course, its performance in the rain. This is where the jacket did not quite meet my expectations.

Rain jackets come with a durable water repellent (DWR) finish on the outside. This is for the sake of breathability, not waterproofing. If rainwater forms a continuous film on the outer surface of a jacket it will act as a barrier to the transfer of air and water vapour from inside the jacket to the outside, in effect killing the jacket’s breathability. The DWR finish stops this happening by forcing rainwater to bead up and roll off.

Discoloration from rain due to the material partly wetting out. In prolonged rain the material darkens uniformly and becomes slick with water

But the DWR finish on my Aeon jacket was quickly overwhelmed by rain, allowing the outer face material to wet out. This may be the reason why my upper body invariably ended up wet through when I walked in prolonged rain during my Scottish trek.

I walked in temperatures of maybe 12 to 15 degrees C (54–59 deg F). When the weather was dry I wore a base layer, shirt and fleece. If I needed to put on my rain jacket I would first remove the fleece, deliberately opting to walk cold rather than overheat. But this did not stop me getting wet under the jacket from sweat or condensation or both.

Opening the pit zips made little difference, presumably because my rucksack shoulder straps did not allow air to circulate under the jacket.
Pit zip (closed)

The jacket itself did not leak except at the sleeves. The cuffs seemed to soak up water which crept up inside the sleeves and got into my waterproof gloves. Because of this I only wore the gloves once on my Scottish trek. Then I didn’t bother with them any more no matter how heavy the rain.

On the basis of my experience I would say that the jacket is hardly breathable at all. I have a Berghaus Light Trek rain jacket which has a breathability rating identical to that of the Aeon, but which performs better. The Light Trek has given me problems with condensation in the past, but nowhere near as much as the Aeon.

The Aeon weighs 77g (2.7oz) less than the Light Trek and it is the jacket I would pack in my rucksack if I were expecting occasional showers. But in the light of my Scottish experience I would take the Light Trek if I were expecting prolonged rain.