The Science of Sleeping Bags

Sleeping Bags

Who wants a cosy night’s sleep? Everyone, right? Even at home your temperature can affect how you sleep. We all have hot water bottles, an electric blanket or different togged duvets depending on the temperature to keep us warm in the cooler months. So, it’s easy to say that the sleeping bag is an important piece of kit to think about. There are many factors to consider when looking at the warmth rating, but we have to start somewhere…

Let’s start with the outside temperature; the season you’re camping in is obviously a major factor. You may have a feeling for what temperatures to expect in the UK, but does that knowledge extend to include the night-time temperatures? In addition to seasonal effects, altitude also has a bearing. It might surprise you to hear that being just a few hundred meters above sea level significantly changes the air temperature.

The other variable to throw into the mix is how the cold affects YOU. Again there are many factors to consider but the important ones are your age, body mass and gender. As a rule, women, those who are slimmer, and the elderly feel the cold the most. Whereas, males, those who are larger, and those in their middle years feel it the least.

So where does this leave you? Pretty confused I imagine. Well fear not, help is at hand. To get you on track we’ve created a system to help you calculate a sleeping bag rating guide for UK camping, but before you get started you need to understand the sleeping bag rating scale.

Sleeping Bag Ratings

Sleeping bag warmth is rated in one of two different scales. Firstly, there are season ratings, and secondly EN13537 ratings. Season ratings (using a scale of 1 to 4) are how bags were traditionally categorised. Starting with 1 Season being suitable for UK summertime, through to 4 Season being suitable for year-round use. Although you will still see season ratings they have largely been replaced by the more reliable and versatile EN13537 ratings.   

For a sleeping bag to meet the EN13537 standard it must be independently tested to gauge its warmth. The test provides a range of temperature information for each bag, but the important figure for our purposes is the Lower Comfort temperature. This is the lowest temperature you can sleep in and still remain comfortable.

To help you gauge your Lower Comfort temperature for UK use take a look at the following table. This is a guide for you to select the correct figure for the time of year you would normally go camping. We’ve also included approximate season ratings in case the bag you are looking at is not EN13537 tested.

Now you have a starting point to work from to adjust your required rating to allow for other factors. The first thing you need to ask yourself is whether you generally feel the cold more. If, for example, you are a slim female who camps from May to October you’d probably want to adjust your rating from 5°C or 2 Season down to 0°C or 3 Season. Alternatively, if you are male and of a larger build you could probably stick at 5°C or 2 Season for the same usage.

The other major factor to consider is altitude. If your prefer campsites in the upland valleys of our national parks you may want to think about an extra degree or two of warmth. If, however, you enjoy wild camping closer to the mountain tops, a more drastic adjustment may be needed. For example, if you were an individual who feels the cold and enjoys upland wild camping from May to October you may find you need to adjust your rating from 5°C or 2 Season down to as little as -5°C or 4 Season.

Finally, for the most extreme camping this formula can be applied beyond our chart. If an average male were looking for a sleeping bag for year-round high level camping his rating would drop from -5°C or 4 Season to something closer to -10°C. 

Well we hope you feel better equipped to choose the right sleeping bag for your needs. Armed with this information and our huge range of sleeping bags we’re confident you’ll not get hot and bothered. Nor will you be left out in the cold on your next camping trip.

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