WHEN it comes to selecting your outdoor gear, few items receive as much consideration as your sleeping bag.
In terms of importance, it’s right up there with your tent, backpack and boots.
As with most modern pieces of camping equipment, sleeping bags come laden with technical jargon; but what does it all mean?
Let’s break it down…
First off, there are a few questions you need to ask yourself before you begin to narrow down what you’re looking for in a sleeping bag. And they are: “What am I using it for, and when will it be used?”
If the answer is “A couple of overnighters in the summer holidays” then your choice will be made a lot simpler, but if it’s “Winter up in the mountains” you’re going to need to understand a whole lot more about your sleep system.
Two considerations should now form your choices in the next step towards choosing your sleeping bag – the shape and style that matches the way you sleep best, and then the all-important ‘comfort rating’.
When it comes to selecting the shape, you may be surprised to learn modern bags come in quite the array of styles – mummy-style, rectangular, semi-rectangular, quilts, elephant’s foot, double, zipless, and female-specific.
Mummy-style has a tapered bottom, saving a few grams on weight and also hugging around the feet and lower legs. Rectangular is what you might envisage as the traditional shape.
Quilts have grown in popularity in recent years as they are often weight-saving and can be configurated in several different ways.
Elephant’s foot sleeping bags are an interesting design as they often only come up to the midriff or chest, and have a tapered mummy-style bottom but sometimes with an extra shape for your feet. They are intended to be used in conjunction with quilted jackets, therefore saving on weight and space due to the reduced amount of material.
The zipless bag utilises layers in a way that has been designed for side-sleepers, while a double is – as you might expect – designed for two people sharing the same bag.
Comfort rating for sleeping bags
There are two standards of comfort ratings for sleeping bags – one introduced in 2005 (EN13537), and an updated version (ISO 23537) in 2017. Thankfully, both systems are quite similar. A further update – ISO 23537-1 – was launched in 2022 to incorporate amendments to clarity and applicability.
EN 13537
EN 13537 provides four temperature ratings to demonstrate how warm a sleeping is, based on the average comfort level of a 70kg man.
EN Upper Comfort – The warmest comfort level, as in the top end of a temperature being in the bag before feeling too warm.
EN Comfort – This is based on the average comfort level of a 60kg woman.
EN Lower Limit – Based on the 70kg man, and the lower temperature of comfort.
EN Extreme – In 2005, the extreme limit (lowest recommended temperature for the bag) was based on the average comfort of a 60kg woman.
ISO 23537
ISO 23537 Comfort Range is expressed as the temperature range within which an average does not feel cold and would be expected to sleep for eight hours in complete comfort.
ISO 23537 Transition Range is based on an average man “in a situation of fighting against cold (posture is curled up inside the sleeping bag), but in thermal equilibrium”.
ISO 23537 Extreme Range states that falling into this temperate means “a strong sensation of cold has to be expected”. The rating warns there is risk of hypothermia, and that the sleeping bag should only be used in this range in an emergency.
NOTE: Several manufacturers will use a hybrid rating system incorporating elements of both EN 13537 and ISO 23537.
Sleeping bag season ratings
Many sleeping bags will offer a seasonal rating rather than go down the technical rating route, but this is simple to follow.
If the sleeping bag is rated as ‘one season’ or ‘season 1’, it will be very thin and designed only for summer use. Two season will be suitable for spring and summer, while a three season sleeping bag will be designed a little warmer and recommended for spring, summer and autumn.
The next level is classed at either four season, or even four/five season (again, this may be presented on the label as season 4, or season 4/5). It’s likely that most manufacturers producing four/five season sleeping bags will also be providing the EN and ISO technical ratings above, and these will be designed for harsh conditions, so it is very important to examine the comfort and extreme ratings provided.
Synthetic versus down sleeping bags
Ever since synthetic sleeping bags were first introduced in the late 1930s (yes, they’ve been around for almost 90 years), debate has raged about which is the best sleeping bag filling – synthetic or down.
Synthetic is by far the most common filling these days, but the purists will argue down has the superior qualities for insulation and weight. The synthetic champions, however, would counter that argument by suggesting their choice is less expensive, more hard wearing, and will perform better in tough conditions.
Essentially, as with most camping equipment, it comes down to personal choice born from a little expert opinion, a touch of research, and a bit of experience.
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