Sleeping Bag Temperature Ratings – Staying Warm in the Wild
A warm sleeping bag is an essential bit of kit if you’re planning your next trip in the great outdoors. There’s nothing worse than being on top of a mountain waking up all night wishing you had bought a warmer sleeping bag. Believe me, I’ve been there! This article will show you everything you need to look for so you can sleep soundly, waking up refreshed and raring to go for another day of hiking or backpacking.
EN13537 – Sleeping Bag Testing & Ratings
In 2005 a new criteria was brought in for all manufacturers, distributors and shops selling sleeping bags in Europe. These criteria tend to apply to most sleeping bags elsewhere, although they may be labelled slightly differently. They introduced a laboratory test to determine the temperature ratings of different sleeping bags to help the buyer choose the most appropriate one.
The test has four temperature categories according to how comfortable you want to be, these are:
- Upper limit – this rating asumes you have your arms out of the sleeping bag, and have the zipper half open. It’s basically the upper temperature limit before you start to sweat (measured for the ‘standard man’).
- Comfort rating – this is basically the ideal temperature – where you can sleep soundly without being too hot or cold (this is measured for the ‘standard woman’).
- Lower limit – basically it’s the temperature where you remain comfortable enough to sleep for eight hours whilst being curled up tight.
- Extreme – you wouldn’t really want to be in your sleeping bag at this temperature, as the ‘extreme’ category is literally the ‘survivable temperature’ where you don’t get hypothermia – it’s making me shiver just thinking of it.
If you wonder why the terms ‘standard man’ and ‘standard woman’ keep being mentioned, it’s because men and women typically have different metabolisms and the European tests take this into account. On average a man is supposed to have a higher sleeping metabolism and so will generally be warmer at night, whilst women will usually be cooler. Obviously this isn’t a universal law of nature, everyone is different and has different temperature requirements. Some people are just ‘hot sleepers’ that always throw the blanket off of them, and others like layer after layer covering them at night.
The tests also assume you will be wearing just long thermal underwear and a hat, what an attractive image! As well as the comfort categories above, there are also simpler ways that sleeping bags can be rated – such as:
- Summer season sleeping bag: 35ºF and higher
- 3-Season sleeping bag: +10ºF to 35ºF
- Winter: +10ºF and higher
- Sub 10ºF – for this category the EN13537 doesn’t apply – they aren’t calculated for this temperature range
Why these ratings might not be accurate
There are a few reasons why sleeping bag manufacturer’s temperature ratings might not actually be accurate – here’s why:
- If you’re a woman or a ‘cold sleeper’ then you might want to add your own personal buffer of 10ºF onto whatever temperature rating is shown on the sleeping bag. This is because the labelling usually assumes a comfort level for the ‘standard man’ – who typically has a higher sleeping metabolism than women. If you’re camping with babies or kids then you’ll also want to opt for a lot warmer sleeping bags specifically designed for kids.
- You need to make sure you’re as close to test conditions as possible to achieve the rating. By this, I mean that you should be sleeping on a good quality camping mat or camping cot. This will insulate you or raise you off of cold ground, preventing heat loss as you sleep. You’ll also sleep more soundly as they’re really comfy, as long as you don’t keep sliding off through the night as I usually do!
- Your clothing – as mentioned before the temperature guidelines assume the sleeper will be in one layer of long thermal underwear. Ironically having more layers of clothes (particularly cotton ones) might be counterproductive to making you warmer. This is because if you sweat it will drench your clothes, and the non-wicking varieties will just leach heat from your body and stop your sleeping bag from insulating you.
How does the shape of the sleeping bag help keep you warm?
There are different styles and shapes of sleeping bag, each one can be used in different situations and is more suited to certain conditions. Here are the most common styles of sleeping bag:
Rectangular Sleeping Bags
These are usually the most comfortable sleeping bags in terms of having extra room and ‘movability’ once you’re inside. By having more room inside though the heat isn’t as concentrated around your body, and they are therefore more suited to summer camping or in warmer climates. Obviously the internal fill material of the sleeping bag will really determine how warm you will be at night, if you’re looking for the warmest type then I’d personally opt for the ‘mummy’ style below.
Another side-benefit of rectangular sleeping bags is that if you have two of them you should be able to zip them together, making them into a double sleeping bag.
Mummy Style Sleeping Bags
Mummy sleeping bags are wider at the head, and taper to be narrower at the feet. As mentioned before the benefit of these types are that they ‘hug’ your body more closely, leaving less room for air, and hence it’s easier for the sleeping bag to keep you warm. 3-season sleeping bags are usually of the mummy type as they are more suitable for lower temperatures.
Those with bigger frames might prefer a rectangular sleeping bag, although you can get different dimensions of mummy sleeping bags that are wider at both ends. Testing certain models out for size in a shop, or at least measuring your dimensions is the best way of making sure the sleeping bag is ideal for you.
Other aspects that affect how warm you are
- Synthetic Insulation – This is cheaper than down insulation below, and is great if you anticipate your sleeping bag getting slightly damp. Obviously any sleeping bag will lose some of its insulating qualities if you get it wet, but synthetic bags are much much better at still keeping you warm. They are usually more bulky than down insulated ones, however they usually cost much much less. Being synthetic they are also non-allergenic, as some people may start sneezing or be allergic to down insulated ones.
- Down Insulation (goose or duck) – Down insulation can provide excellent heat-trapping properties. It is expensive, however it has amazing qualities compared to synthetic materials. Not only is it exceptionally lightweight, it is compact and provides an excellent weight to heat ratio. Goose down is the traditional and possibly more efficient of the two, however duck down is also becoming a lot more popular. Not all down is created equal however – down with a higher ‘fill power’ will require less of it to achieve the same temperature rating. So your budget will probably dictate how compact a sleeping bag you can afford.
- Water Resistant Down – if you’re willing to pay a higher price then some brands offer water resistant down sleeping bags, giving you the best of both worlds. The insulating qualities of down, with the water resistant properties of synthetic materials.
Sleeping Bag Length
It’s not always a good thing having too much room in your sleeping bag. If it’s too roomy, or too long, then it won’t keep you the warmest. When you’re looking for a new model then be sure to choose one that has been designed for your height.
Sleeping on bare ground is no fun at all – get a proper sleeping pad or camping cot to have a comfy night’s sleep. Some are padded, others are inflatable, and even these come with insulation ratings. If you pick a good one then it will really pay dividends.
The better quality sleeping bags have lots of integrated features designed to keep you even warmer. Each one might only add a tiny amount of insulation, but combined it can all add up. Drawcord hoods wrap around the top of your head to minimise heat loss (30% of heat loss can be through your head!). Draft collars, neck baffles and draft tubes are also little extras to look out for that can keep you that bit warmer.
Although sleeping bag temperature ratings are largely standardized, as we’ve discussed it’s important to consider your own particular physique and metabolism in choosing the model best for you. The type of camping, tent you own, weather, climate and ‘packability’ are also important factors to consider. I hope this article has helped you in finding the best model for your needs, if you have any comments then I would love to hear from you below. Happy camping!