An unusual highly breathable down/synthetic midlayer

This unremarkable looking jacket is actually quite revolutionary. It appears to be another quite light quite warm insulated jacket. It isn’t. It performs very differently to most such jackets. In particular it’s extremely breathable and not windproof in the slightest. It’s designed to be a midlayer that allows moisture through very quickly whilst providing the warmth of a much heavier fleece jacket. This isn’t a warm windproof jacket to pull on over all your other layers.
The jacket is filled with a new 750 fill power down/polyester mix called ThinDown. Producing this involves fusing the two materials to make a sheet of 52% down/48% polyester material that is said to be 30% warmer than 100% polyester insulation and also more compressible and much more durable. Because of the stable structure ThinDown doesn’t need a downproof shell unlike standard down. Berghaus has used a soft stretch polyester/elastane material for the outer and says the Aonach has up to 50 times the airflow of a standard down jacket. The first thing I did when the jacket arrive was blow through it, which I can do easily. It’s hard to blow through even ultralight down jackets.
The design is fairly standard. The Aonach has a neat stretch hood, handwarmer pockets, and stretch cuffs and hem. There’s no chest pocket, which I’d like to see for carrying a map or phone – especially the latter as it’s best to keep one warm to save the battery. The insulation isn’t the same thickness throughout but is concentrated in areas where it’s most needed. Look closely at the jacket and you can see stitch lines through the thinner areas in the centre of the back, down the sides, and on the front of the shoulders. Over 50% of the fabric is recycled and over 90% is bluesign approved.
The Aonach Jacket and ThinDown sound wonderful. The key of course is performance. And I’ve found it does perform as claimed. The jacket really is very breathable. I’ve worn it all day under a waterproof jacket and haven’t overheated or had much condensation inside. The jacket really isn’t windproof either, a slight breeze cutting through it. It’s also very warm for the weight.
I’ve been trying the Large size Aonach jacket, which weighs 555 grams, the same as many midweight synthetic insulated jackets and fleeces. It’s reasonably compact to pack and can be rolled up inside the hood. Here’s the jacket in use.

This picture was taken when I’d stopped for a break after a long ascent. The air was freezing but there was only a slight breeze so during the climb I’d just worn a windshell over a merino wool base layer. When I stopped I was slightly damp from sweat and quickly started to cool down. I donned the Aonach over the windshell as I would have done with any insulated jacket. However shortly after taking this photograph I started to feel chilly as the breeze was coming through the jacket. Putting the windshell on top solved this and I kept that combination for the rest of the day. I did have a little dampness in the arms of the Aonach, due to pushing myself along with my ski poles I think, but I only noticed this when I took the windshell off and it did dry very quickly.

On this very windy day with a mixture of sunshine and light snow showers I wore the Aonach Jacket under a waterproof all day. I chose the latter in order to see whether condensation would occur. It didn’t. I stayed warm and dry, an impressive performance from the Aonach Jacket.
I’ve only worn the Aonach jacket in freezing weather so far. I suspect it’ll prove too warm once temperatures start to rise. I think the warmth is roughly comparable to a heavyweight fleece or a midweight synthetic insulated jacket, both garments I find too warm for walking in for most of the year. The excellent breathability should give the Aonach quite a wide temperature range though so I may find it cooler than I expect. As it is though who walk in thick fleeces or insulated jackets regularly may well find the Aonach jacket a good choice most of the year.
ThinDown is exclusive to Berghaus for the next three years. The Aonach jacket won’t be available until the autumn.