If you've seen the blurb from Sea to Summit (STS) you'll know that the key feature of their mats is the 'pocket' style construction which they claim is more comfortable than other mats because it mimics the way your bed at home works. I was keen to try this new construction but most of the mats are quite a bit heavier than the competition and so settled for the Ultralight Insulated model which compares quite well with others I've used for backpacking although its not the lightest.
One reason this mat is heavier is that STS have settled on 40D fabric, this compares to lighter competitor mats which use 30D or 20D fabrics, the STS mat is therefore a more robust choice.
One concern I had was the thickness, about 20% thinner than comparable mats and that usually means less comfortable, though I have to say I needn't have worried - although sleeping on this mat felt different - it was no less comfortable than other mats I've used in the backpacking category. That means the construction method must be working - which suggests that the heavier models with more sophisticated versions of the air cell construction must be supremely comfortable!
I spent 15 nights sleeping on the mat, going to bed around 7pm when it got dark and not getting up until 6am the following morning, that's a long night, which further confirms just how comfortable a mat it is.
I took a Sea to Summit Airstream Pumpsack as an accessory to the mat, it weighs just 52grams and you can use it as a drybag as well as its main function which is to blow the mat up. Blowing it up using your mouth is fine at sea level, but at 4800m its an effort that's worth avoiding if you can. The Pumpsack works very well indeed, you connect it to the inflation valve, allow air into the sack, close the end and compress the sack forcing air into the mat. The mat was fully inflated in three or four goes and it really was very easy to use.
Another surprise was the ease of deflation - the mat uses a dual valve - it has two possible opening options - the first is a non-return valve for inflating the mat without air leaking out when you stop blowing - the second is the deflation valve which opens completely and the air vacates the mat in an instant. I'm pleased to say that the supplied stuffsack is the right size (!) and its not a daily nightmare trying to get it back in like some mats.
Anecdotally the mats slide characteristics seem pretty good as well, again comparing it to other mats I've used it was probably a bit less likely to move about the tent than the lightest options.
As far as insulation goes we had a few cold nights and mornings. I was using a STS Spark III sleeping bag which has a comfort limit of -4C, we recorded temperatures as low as 2C on some mornings and I was able to sleep comfortably in a thin baselayer and socks - I wouldn't have been able to do that without a decent insulated mat. I wouldn't hesitate to recommend it for just about everything but camping on snow.
Finally I can't end this review without mentioning the Air Chair Kit - 228grams allowed me to relax each evening in a comfortable seat with a supportive backrest - while there was definitely a 'knack' to getting it setup once it was working it was worth its weight in gold - I've reviewed it separately, follow the link.
The Ultralight sleeping mat range has a single layer of medium resolution Air Sprung Cells™ to give you the lightest and smallest packed-volume mat without compromising comfort. To add warmth, we use Exkin® Platinum, a quiet non-woven fabric that reflects radiant heat loss back to the user and Thermolite® insulation to prevent convective heat loss between your body and the ground.