Thermarest Altair 0F Winter Down Sleeping Bag Review 2014/10/14

The Thermarest Altair 0 (-18C) is a goose down sleeping bag with some interesting features that separate it from other products available and make it a purchase certainly considering. Read our full review and field test of the Thermarest Altair Winter down sleeping bag.


For activities in the cold dark months of the year when frost and seeing your breath in the air are common place, warmth is an important component of your kit list. Especially at night. The Thermarest Altair 0 (-18C) features a very warm fill of goose down, rated at +750. This fill power is just below that of the highest spec down bags, normally rated at +800. However the Altair has a very high quality fill none the less.

Fill Power

The +750 goose down allows the Altair to go down to limit of comfort -11C with the extreme rating at -31C which means the bag can keep you warm in those winter temps in the backcountry and in the mountains and as long as you are not going into really high altitude ranges then the Thermarest Altair will keep you toasty. Thermarest have stuck these big elastic bands on the back of the Altair to help secure the roll mat in place beneath you. Preventing you and the sleeping bag from moving independently and as a result falling off the roll mat. This is a great idea which works well in practice. I normally at least once a night get a cold arm as the roll mat has moved and I am left with part of me just lying on the ground but with the Thermarest Altair it doesn’t happen.


Insulation is constructed in box baffles and is zoned, meaning there is more fill on top of you than beneath you. Anything that gets compressed by your weight when you lay on it does not help to keep you warm as you have forced all the air out of it.

The cut of the Thermarest Altair is very spacious at the top and at the hips allowing for a non-restricted night’s sleep. On the other hand it's nice and snug at the feet to eliminate excess bulk when packing.

The face fabric also has a DWR (durable water repellent finish) to help keep condensation off and is made of nylon which is very strong.


Weight of the Thermarest Altair is just over a kilo at 1.2 kilos. I think that is pretty good for the temperature the bag can take you down to.


I have used the Thermarest Altair out in Northern Sweden in -18, Finnish Lapland in -20 and on those slightly chilly nights back here in the UK. It is one of the best sleeping bags I own and I am always comfy when sleeping inside it.


One area I wish was different however was the stuff bag, which lacks any compression straps and is rather large. What I have done is simply use another branded compression bag with not only straps but a floating lid. With this I can get the Altair down in an even smaller pack size! Once you have done this step the Altair becomes a really great bag! Highly Recommended


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