How warm does my sleeping bag need to be?

By Hati Whiteley

How do sleeping bag comfort ratings work? A quick answer would be to say… hmm, maybe there is no quick answer, except that you should take sleeping bag comfort ratings with a generous pinch of salt.

A sleeping bag comfort rating is a helpful guideline, but that’s all it is. How comfortable you actually are in your sleeping bag depends on how you use it, where you’re going, what you’re doing, along with a plethora of other factors.

The most important thing to remember is that you are your heat source. A sleeping bag can’t burn energy to heat itself up: that’s your job. All that a sleeping bag can do is provide insulation and ensure that the heat you generate stays in the air around you.

So, what should you be thinking about when picking a sleeping bag? Well the Customer Service Heroes have all the answers…

How do you sleep?

Do you sleep warm or cold?

You know that person who always needs an extra blanket, even when everyone else is sweating under summer duvets. Does that sound like you? If so, you will need more insulation from your sleeping bag and should be looking at a lower comfort rating.

Will you be doing more exercise than usual?

When you’re tired and hungry after a hard day of physical activity, your body is lower on energy than normal and will struggle to keep you warm through the night.

If you're not used to physical exertion (especially at altitude) you may need to look at sleeping bags with lower comfort ratings.

Do you wriggle or move about in your sleep?

A sleeping bag retains your body heat by trapping warm air around you, so moving about a lot in your sleep causes it to push warm air out and suck cooler air in. Although sleeping bag baffles reduce this, fidgety sleepers will need a sleeping bag with a lower comfort rating.

Some technical sleeping bags have less insulation on the base than the top. The logic behind this is that the insulation is crushed when you lie on it, so why bother with putting as much there? However, if you move around during sleep, less insulated panels could end up being on top of you and the more insulated top sections crushed underneath you.

Are you used to living in the temperatures that you plan on using the sleeping bag in?

If you live in Norfolk and follow the sun like a sunflower, your body will find cold conditions more difficult to adapt and respond to. This means that you may need to look at sleeping bags with lower comfort ratings.

You can get around this by exposing your body, in particular your extremities, to colder temperatures, thereby giving yourself time to acclimatise. For example, before Alpkiteer Paul Errington set off on the Arrowhead Race in Alaska, he sat in front of the telly with his feet and hands in buckets of iced water.

What will the conditions be like?

How humid will it be?

UK weather tends to be humid, making temperatures around zero feel much colder. In contrast, the drier air of the Alps and other large mountain ranges can almost feel warmer that they are, making the Alpine feels-like temperatures not unlike UK conditions.

How high are you sleeping?

Sleeping on the top bunk probably won't have much effect, but even one night at altitude can deplete your body’s energy stores as staying warm uses more energy. To compensate make sure you eat and drink more to keep warm.

How cold is the ground?

Conduction through the ground is the quickest way to lose heat whilst sleeping. If you are sleeping on frozen ground or snow, it is worth investing in a good sleeping mat as well as a sleeping bag. (Read our SLEEP guide for more on winter sleep systems)

How will you use it?

Does the sleeping bag need to be compressed for transportation?

Most people think their sleeping bag needs to pack up as small as they can make it, but you should only really pack it as small as is necessary.

The more you compress a sleeping bag, the longer it will take for the insulation to recover to full performance. Many lightweight backpackers are beginning to opt for larger, lighter rucksacks and, rather than filling them with more kit, they compress sleeping bags and down jackets as little as possible

Can I keep my sleeping bag dry?

A wet sleeping bag will always feel cold; in fact, a wet down sleeping bag will have almost no insulation to it at all.

For this reason, many people are deterred from buying down sleeping bags. However, most of us can keep a sleeping bag dry enough to retain most of its insulation… plus it takes a surprisingly long time to wet it out.

It is little-known that a sleeping bag retains a lot of your bodies perspiration, especially if used in a bivvy bag. Although in warmer weathers this isn't a problem because the sleeping bag stays warm and the perspiration simply evaporates, in sub-zero conditions that sweat can freeze around the insulation. After one or two nights, this may be negligible, but during continued use without intervention you will begin to feel the effects.

You warm the bag

No matter how thick and fluffy your sleeping bag is,YOU WARM THE BAG! This means that you need to think about what you will eat, when you will eat, what you will drink, when you will drink, how you will stay warm, when you will go to bed… The list isn’t quite endless, but there is a lot to think about.

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