Choosing a sleeping bag

21 April 2012

You're on the side of a hill and it's 2.37am and I know you've said these words:

'Why do they call this bloody thing a sleeping bag again?'

Then, during the course of the next 2 hours, you continually mutter things about the 'trade descriptions act' and 'insomnia bag more like' while watching the sun rise through your eye lids and fly sheet.
Choosing a sleeping bag
Does this mean you've bought the wrong sleeping bag?

Not necessarily. The sleeping bag could be the problem but then again there a few other things to consider.

With the vast assortment of sleeping bags on the market it is sometimes difficult to make a decision. I'll try and help.
So let's go through the basics.
Sleeping bags keep you warm at night. That's simple enough. And the way they do it is to slow down your heat loss. You supply the heat and the sleeping bag stops it escaping. We all know that, so let's discuss how much insulation you need in your sleeping bag.
Sleeping Bag InsulationSleeping Bag Insulation
The amount of insulation you need is a difficult subject, because it depends if you 'sleep cold' or 'sleep warm'. Here's an example, if your bedroom window was painted shut in 1973 and you normally sleep with your thick teddy bear jimjams button all the way up to your nostrils then I would hazard a guess that you 'sleep cold'. In this case, you need to buy a bag with a little more insulation.
Your friend, who lies naked on top of the duvet with a stiff December breeze blowing through his skylight, may sleep a little warm and I would suggest a little less insulation.

The easiest way to find out the amount of insulation in a sleeping bag is to check the Temperature Ratings of the bag.
Temperature Ratings
If a sleeping bag has a Temperature Rating rather than a Season Rating then the sleeping bag has usually been tested under laboratory conditions.

Gelert sleeping bags have been sent to the Hohenstien Institutes in Germany to conform with EN 13537 standards. The EN 13537 test is conducted under controlled conditions using a mannequin in the sleeping bag that has separate heating zones and temperatures sensors to simulate a human body in a sleeping bag. These figures are a guide and should only be considered 100% accurate if you are actually a mannequin.

The sleeping bag extreme temperature rating is the lowest temperature at which the bag will perform. This figure, for the average user, is pretty useless. This rating is intended to show the minimum temperature at which an experienced user could use the bag to stave off hypothermia.
Temperature Ratings
The figure that is most useful is the lowest figure in the comfort zone rating. This figure is the one you should use when you ask the question: how cold is it likely to be where I'm going?!!
Guidelines for the UK
Roughly in the UK, I would say the lower comfort zone figure for the different seasons should be the following:

Spring: 0 degrees C
Summer: +7 degrees C
Autumn: -3 degrees
Winter: -7 degrees

If you're going to colder/higher regions then a little bit of research into the area is required before you decide.

These temperature ratings are only guidelines because there a many other factors involved in how warm you will be.
Warm or Cold Sleeper
Firstly, as we said earlier, subtract a few more degrees off the sleeping bag comfort range if you regularly sleep in your cozy toes bed socks. Add a few more degrees and get a bag rated for warmer climes if you like a gentle wind on your oxters.

Women in general need a sleeping bag which is 5 degrees warmer than men. I don't know why. Jacqui in the office will take offence at this, but I'm not just making these figures up.

Also, older people may also need a warmer sleeping bag than people in the 20-40 age group. Hardened mountaineers are usually more comfortable at lower temperatures than a complete novice.
How to feel warm nakedHow to feel warm naked
!Also, decide what you are going to be wearing in the bag. Manufacturers usually assume you will be sleeping in a baselayer set of some description.

If you like to wriggle in naked, firstly don't pull the zip up too fast and secondly buy a slightly warmer bag - unless you're a warm sleeper then leave it as it is. See I told you I can make anything complicated.

The opposite applies if you like sleeping in your full wardrobe.
What will you be sleeping on?
A lot of body heat can be lost into the ground if you don't choose the correct sleeping pad.

Different types of mat have different R values, which is a measure of insulation. Choosing a sleeping mat is a whole different discussion which we will go into another time, but when buying the sleeping bag bear in mind heat loss through the ground and the quality of your sleeping pad.
Does it fit?
Check the fit. Make sure it's long enough and wide enough, otherwise at least one of your extremities is going to be sticking out and get nippy.

I've made the photo on the right small - I don't want your gouged out eyes on my conscience

Mummy shaped sleeping bags fit more closely round the body to give less air space for you to warm up, so they are more thermally efficient. Square Sleeping Bags are less thermal efficient because they have more room but you can kick your legs about like you would at home.
Does it fit?
Eat makes Heat
Sorry, tried a bit of 'Eat' 'Heat' word play there in a feeble attempt at a catchy phrase - came out naff but it'll have to do.

Before you go to bed, no matter how tired you are, always have some grub. The more tired you are the more important it is to refuel. When you eat, your body gives off more heat which gets trapped in your correctly rated sleeping bag and keeps you toastie.
A bit of romance to finishA bit of romance to finish
If you're having a romantic camping weekend with a partner who doesn't mind your stinky feet and your amorous advances, then you're on to a winner in more ways than one. Snuggling is the best way to keep warm. So buy a lesser rated sleeping bag, so the apple of your eye is cold... only kidding.
Other considerations
Like a said at the beginning, this is just the basics of choosing a sleeping bag. There are many other things to consider like pack size, whether you want synthetic or down, does it have a waterproof shell, does it have a hood and neck baffle, will you be using it with a bivy or tarp, plus many more. But we'll discuss that another time, because I know you're getting bored now.

Thanks for reading.

Ian Young

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