For this current Siberian winter bike trip I’m using a Cumulus down sleeping bag. It’s the one I used in Scandinavia last winter. It worked great then. But I didn’t get the opportunity to really test it to it’s extreme. Now I have.
The bag I’m using is the Cumulus Excuistic 1200. It’s made with 1200g of 850cuin polish goose down, weighs just 1770g and is rated at -21C comfort, -32C limit and -46C limit.
In Scandinavia, it got a lot of use, down to -30C and I slept very well. Much milder than -15C and I was too warm and had to unzip it. For more on my sleeping set-up (with vapour barrier and bivvy) - see the earlier review here.
In Siberia, I have now bivvy’d out at -50C. I was not cold. Well, my little toes got cold, but I guess I could have just worn a thicker pair of socks. I always have cold feet. So, no tent, just a bivvy bag (no vapour barrier sack – mine split) at -50C – and it was fine. Note that camping at -50C is not generally pleasant – being inside the bag was the only time when I wasn’t struggling with cold hands (or feet)!
The bag is thicker on the top side, with less down on the underside where it would only get compressed anyway. This is to save weight. It is also thicker at the feet, which tend to get colder. All-in-all, this bag is one of, if not the lightest, cheapest bags on the market for it’s temperature rating.
I would say that the rating is conservative considering what I have slept in it now.
For the details – you can choose whether you want a left- or right-sided zip. The hood is cozy and there is a toggle to tighten up. A baffle velcros around your neck so that all your body heat is contained within the bag – that, afterall, is how the sleeping bags keep you warm; by using your own body heat. My only complaint, and it’s a minor one, is that the velcro on the baffle could be wider as sometimes it comes unstuck during the night if I have tightened up the toggle (too much).
There is very little more I can say – it does exactly what it is meant for. It does it well. And what’s better, it comes with a 10-year warranty.
For me, I want gear that works well. I don’t want to have to think or worry about it. So if you know what temperatures you will be sleeping in – head straight for Cumulus and select the one at the required rating and you won’t go far wrong.