I’ve been struggling for a while to come up with some meaningful way to rate the warmth and comfort of sleeping bags, and drawn a bit of a blank. I’ve experimented with thermometers, hot-water-bottles and all manner of sleeping positions, and decided that there’s much, much more to how good a sleeping bag is than any rating. You realise when you read -10C on a sleeping bag’s label and then freeze to death in a single-skin tent on a chilly autumnal night that numbers are pretty much only the start of things to consider.
Nanok has a rather refreshing way of explaining what their sleeping bag numbering system means in terms of your night’s sleep. Here’s an extract:
• In the temperature range of +15 C to -5 C it is expected that you will wear short underwear and a T-shirt in your sleeping bag.
• In the temperature range from -5 C to -20 C you are expected to wear a thin “1st layer” that is normally a set of thin, long woollen underwear.
• When it is colder than -20 C you will normally use a thin 1st layer and in addition a 2nd layer on your upper body.
• Women should add 4-5 C to the comfort temperature in outside temperatures down to -15 C.
• Women should add 8-10 C to the comfort temperature in outside temperatures below -20 C.
• Those older than 30-35 years you should add 5 C to the comfort temperature.
• If you are going to altitudes above 3.300m you should add 5-10 C to the comfort
That seems fairly sensible, and the Norwegians should know a thing or two about how to deal with the cold. It also explains why the Wife is always cold, since going by the above she should be adding 10C to any sleeping bag rating.
Beyond pure rating, the Nanok Airlock has a couple of tricks up its sleeve. Firstly is its construction, which is in two parts. Nearest your skin is a layer of soft, air-trapping down which insulates your body-heat and keeps you toasty. Then the outer layer of filling is a synthetic fluff, which traps some of that heat in and protects the down from moisture and insulates you if it does get wet.
The outer skin of the Airlock is a waterproof and breathable fabric, which means that you’ll be OK if your tent springs a leak, or if you’re forced to sleep outdoors in anything but heavy, prolonged rain. One note – the seams of the bag aren’t taped, so it will eventually leak if you DO sleep in a storm – you’ll need a bivi for proper overnighting.
The other trick that the Airlock has is a fantastic internal baffle, which is like a soft sausage-dog that cuddles up around your neck and shoulders. What this does is makes sure that all that nice warm air you create in the night doesn’t easily waft out of the bag if you roll over. It works well and feels really comforting.
You notice when you try to put the Airlock back into its stuffbag just how much air it traps inside itself. It’s more akin to rolling up a self-inflating mattress than a sleeping bag. That goes some way to explaining why it seems much warmer than it is rated for.
The fit of the Airlock is slim, in a Mummy-bag fashion. I like feeling surrounded and enclosed by my sleeping bag, but the Wife hates it, so bear that in mind if you’re purchasing online. That said, the feet area, which is sewn in a box design, is quite generous, so you can throw your morning base-layers down there to keep them warm. It’s 195cm long, so 6fters will be OK.
The zipper is a chunky, positive number with two sliders so you can air your feet if they get too warm… or put on your socks before you get out of the bag! It has a large velcro cover at the top and an easy-to-find-in-the-dark pull tag.
The hood is large and closed in easily by a bungee drawstring. It’s not the easiest thing to pull tight, but it does work.
Official rating for the -10 Airlock is (EN13537) -2C Comfort/-8C Limit/-25C Extreme and (ISO TR11079) Comfort -10C.
SUMMARY: A very warm, waterproof and breathable sleeping bag which due to the brilliant baffles feels warmer than you might think from the rating. It’s a comfortably proportioned mummy bag and although it won’t win prizes for weight or size it is a serious piece of kit. It’s very well priced for its quality and rating.
NOTE: The -10C has been replaced by a more UK-friendly -5 version, which retails at £140 and is a bit lighter with 550 weight filling.