How to Choose a Sleeping Bag

By Dave Roberts   

on February 3, 2015    No ratings yet.

How to Choose a Sleeping Bag

Choosing a sleeping bag can be a pain! Here are the main things to consider when buying a new sleeping bag for wild camping.

Shape – You’ll probably go for the mummy shaped bag for wild camping. You’ll struggle to find any other shape for a serious bag, with a few exceptions (quilts and half bags, and perhaps those weird ones with arms and legs!)


Down v synthetic.

What’s used to insulate your bag will affect most of the factors mentioned later. Down is lighter, less bulky and more expensive than synthetic fills. So a given weight of quality down will usually keep you warmer than the same synthetic, all else being equal. You can get better quality down, for more cost that’s even warmer. The downside is that it’s useless when you get it wet, whereas synthetic still offers a degree of insulation as well as not absorbing as much water in the first place and drying out much quicker.


Season or Temperature rating.

When you intend on going camping is crucial. All sleeping bags come with a temperature rating, and have been standardised in the EU under the EN13537 Standard. It’s often difficult to determine what they really mean, but a staring point is to ignore the extreme temperature ratings! You really don’t want to be out on a mountain with sleeping bag while the temperature is anywhere near the bag’s ‘extreme temperature’. With any luck you’ll survive. Many manufacturers only quote the Comfort and Lower limits as the others can be misleading.

For instance:

  • the upper limit is the highest temperature at which a ‘standard’ man can sleep without excess sweating.
  • the comfort rating is based on a ‘standard’ adult woman having a comfortable night’s sleep.
  • Sweet spot – right here!
  • the lower limit is based on the lowest temperature at which a ‘standard’ adult man is deemed to be able to have a comfortable night’s sleep, curled up!
  • the extreme rating is the temperature at which a ‘standard’ female can ‘survive’ for eight hours without hypothermia. As mentioned already, it’s not advisable to rely on this rating!


This test is completed with a mannequin in order to determine how much heat loss the bag prevents (details and maths here). It’s a guide only, and who exactly are these standard men and women anyway*? Of course, everyone’s different! Note that the standard rating differentiates between a ‘standard’ man and woman, with the man requiring less insulation than the woman.  A bag rated at 0°C might be toasty at -5°C for one person while too cold at +5°C for another. You’ll have some idea of whether you sleep cold or not, so you know whether you need to overcompensate with a warmer bag or not. Just remember that it’s always better to have a warmer bag than one that’s too cold! The fit of the bag also has an effect. You want a bag that’s snug, but not too tight as to compress the insulation. Too loose and you’ll lose heat. Some bags can be purchased in varying lengths and widths, which can help eliminate these problems and make the bag more efficient.


If you want something that works from minus to plus twenty, then you may need to invest in a couple of bags, at least. Using bags that combine gets over this problem. I use the PHD Minim Combi and a PHD Minimus which are effective from -18°C up to typical UK summer conditions on the hill. This gives me, in effect, three sleeping bag options. You’ll need something cooler still if you want to cope with warmer climes.

PHD Combi Bag

Sometimes, you’ll see bags sold with a ‘season’ rating. This could mean almost anything, and try and determine the proper temperature rating. As a guide only, here’s what the ‘season’ ratings generally mean, but use with extreme caution!

  • 1 season – Warm summer weather only!
  • 2 season – Primarily a summer bag, suitable for late spring and early autumn.
  • 3 season – Good option for spring-autumn use in the UK.
  • 4 season – OK for most UK winters.
  • 5 season – Expedition!

Full or half zip, or perhaps no zip! The final one sounds ridiculous but works really well, and reduces weight as well as making the bag a bit warmer by eliminating the zip cold spot. Zips can make it easier to get in and out of the bag as well as offering a vent, making warmer bags a bit more usable in warmer weather.

llyncwn 057

Weight and cost. You certainly pay to reduce weight, as it’s usually achieved by more expensive down that’s simply warmer for a given weight. However, you can still find bags that strike a reasonable middle ground. Often they may only be a few 100g heavier, but the price saving is significant.

You can also save weight by taking a half bag (pied d’elephant), or even taking just a quilt. PHD seem to be one of the few companies offering these options, but you need to use these carefully. Half bags work by keeping your lower body warm, and rely on a warm insulating jacket to insulate your upper body. On the plus side, they’re one of the cheapest ways to reduce bag weight as you’re simply getting half the bag!

There are also bags that have been halved by not having insulation on the bottom. The theory being that the insulation there is compressed, cannot loft and is less efficient. Of course, a decent sleeping mat is essential!

Ideally – a summer bag will weigh around 5-600g, with a winter one being twice that. Of course, it fully depends how much you want to spend and you won’t get much below 400g for a summer bag that’s still usable for mere mortals in a typical UK summer.


Bulk – Winter synthetic bags can be huge when packed, and you’ll need to ensure you’ve got enough room in your pack. If not, then you’ll have to choose between going for a down bag or investing in a larger pack! Down wins hands down in this respect, and there was no way we’d have been able to go wild camping on Snowdon with the world’s lightest backpack using a synthetic bag. It would have taken up the entire 20 litres!


Just to give you an idea – here’s a winter and a summer synthetic bag compared to a 35l day pack that is usually sufficient to carry all my gear on an overnight summer trip.


Unfortunately – we haven’t a shot with a down bag to compare, but here’s my PHD Minimus compared to an OS map as a rough idea!


Bottom line? If you can afford it, go for a down bag. Yes they may not be as efficient in the wet, but if you get your bag that wet you’re in for a miserable night anyway! Synthetic is fine if you’re on a tight budget, but you’ll have to put up with the added bulk and weight.

*For the purpose of these measurements, a “standard man” is assumed to be 25 years old, with a height of 1.73 m and a weight of 73 kg; a “standard woman” is assumed to be 25 years old, with a height of 1.60 m and a weight of 60 kg. – Wikipedia, and here!

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Dave Roberts

Dave Roberts founded Walk Eryri in 2004, with the aim of providing routes that are off the beaten track. Walk Eryri is now part of Mud and Routes which continues to provide more off beat routes and walks in Snowdonia and beyond. Dave has been exploring the hills of Eryri for over thirty years, and is a qualified Mountain Leader. Dave also established Walk up Snowdon, Walk up Scafell Pike and Walk up Ben Nevis just to mention a few.

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