A buyers guide to sleeping bags
08 November 2008
Note: Many of these articles are very old, and although the technical information is still relevant the equipment mentioned may not be (for example a Stormy cooker was state of that art in 1995, but not in 2021).
If you don’t sleep well, then your performance will be reduced, and all that hard training and planning will all be for nothing. A fitful night will lead quickly lead to low morale and enthusiasm for the adventure and a mindset that wants to find a nice warm bed. The worst-case scenario is that if you do sleep - not because your sleeping bag is comfortable - but because your suffering from hypothermia, then there’s a good chance that you won’t have to worry about low energy levels the next morning or any morning because you’ll probably never wake up! Your sleeping system is crucial whatever you do, and this article sets out to help you make the right choices so that sleep will come easily…and so will the morning.
Firstly let’s break down the main sleeping bag users who will be reading this article so you know if I’m talking about you.
If your idea of a mountain is the pile of dirty chalk dusted T-shirts and bouldering pants in the corner of your room, or your only interest is avoiding paying for bunkhouses, campsites or B&Bs, then you’re probably a climbing doser. For you, a sleeping bag is something that’s thrown out of the boot of a car into a bus shelter, mates floor or a limestone cave that smells like a public lavatory.
You’re in the Festival category of sleeping bag purchaser and will probably be best served by a bag bought at Argos, Millets or your local mouldy army surplus shop (green’s a good colour if you’re to avoid park wardens or rangers). Get something cheap and thick (synthetic) and leave it un-stuffed when not in the boot of your car. Ignore bags with the name “Moon” in the title that look like they are designed to keep the juices in chickens and promise to keep to warm down to absolute zero, which should actually be read as the total number of hours you’ll spend sleeping comfortably within its clammy confines.
You’ve moved on from the Dosser phase, and now you enjoy travelling and camping, both in the UK and abroad, in order to go climbing. You only camp in a tent, but often use out of the way spots, meaning you need to carry in all your gear. You’re are a serious user who needs a light and compact bag that will be guaranteed to keep you warm so you know you can have a good nights sleep. You aren’t interested in wearing all your clothes in your bag, so you want something that will be comfortable in winter and summer in just your underwear.
A budget down sleeping bag with a fill of around 600 to 800 grams will be ideal, or a medium weight 1.5kg/2kg synthetic bag, keeping you comfortable over a broad temperature range. In summer the bag may be too warm, but if you use a thin liner (crucial with a bag that will be used a lot without clothing), then you can use this instead of the bag on the hottest nights. If you sleep in a very broad range of spots, such as trips to Scotland in Winter and Spain in the summer, then you may be better of with a two-bag combination, using a thin summer bag with a medium weight bag, meaning they can be combined or split depending on the temperature.
You need a bag for long climbs that is as light as possible, yet also be warm enough for long stays in the mountains on approaches to climbs, plus camping in the valley while you sit out bad weather, which you’ll probably be doing 99.9999% of the time (needs to be mould resistant).
The ideal approach is two have a valley bag and a climbing bag, with the valley bag being perhaps a cheap synthetic bag – 1/1.5kg - and the lighter bag a top quality down bag – which ideally would have a fill of around 300 grams. If you want one bag to do everything then a 500-gram fill bag will probably do it, with the only downside being that if your bag gets soaked you’ve got nothing to sleep in once back at the campsite.
If you climb in the alps in the wintertime or are heading for the greater ranges and lower temperatures, then getting the right bag is crucial, as you may be spending many nights out in seriously cold conditions, and as a friend once said to me, “If you don’t have a good sleeping bag you will soon envy the dead!”
Firstly you need to decide if you’re going to be wearing all your clothes in your bag and if you’re going to be using some kind of tent or bivy shelter? If so you can probably get away with a 600-gram fill or 1.5/2kg synthetic bag on most routes. If you’re going to be out in the open or climbing in the severe cold (-20 and below), then you should go for a 1000 gram or more down bag.
The right bag will keep you warm in the coldest temperatures you will encounter and keep you from sweating at the opposite end of the scale. Unfortunately the broader the use the harder it is to achieve this, something compounded by living a climate that is erratic. You may want to camp in Glencoe in January, where the temperature could drop to -10 (although it will feel colder than the summit of Denali), and then a months later sleep out on Lundy where the temperature could be +30. You also need to take into consideration weight, pack size, price and robustness, and it’s a very lucky climber who can balance all of these things.
Down affords the greatest warmth-to-weight ratio out there. It breaths well, meaning the bag feels more comfortable in hot weather, it packs down smaller than any man-made fibre, and perhaps most importantly lasts for many years and can be brought back to life by specialist dry cleaning.
Down is expensive, meaning a greater outlay, to begin with. It can also cause an allergic reaction among some people. The ultra-fine structure of down means it is easily compromised by moisture, meaning once wet your sleeping bags warmth will be severally decreased, plus it can take a long time to dry.
Modern synthetic fibres such as Polargaurd 3D and HV, provide a man-made alternative to down that is getting close to matching down in bulk and warmth for weight, but not quite. This filling is around 30% cheaper and the quality is more reliable and not dependant on finding good quality birds. Most important of all synthetic fibres are highly resistant to moisture, meaning a synthetic bag will maintain the majority of its insulation even when wet.
Synthetic bags do not drape as well as down bags, feeling more stiff and fewer luxuries. Furthermore, they do not breathe as well, meaning that will feel more uncomfortable in hot weather. A lower-cost is also offset by a lower life span, with even the top bags having a steeper drop off in loft over down bags. Another problem is that generally there are very few synthetic bags on the market that match the build and material quality of top-down bags, important if you want the highest level of performance.
I use the term loft to cover both down fill power and synthetic loft. Down fill power is a measure of how much volume is taken up by a given quantity of down. The higher the fill power the loftier the down, loft meaning the amount of air held within the material, which translates into insulation, as still air is a great insulator. Fill power is determined by the number of cubic inches a small amount of down occupies. The down is fluffed up by an air blower, then kept at a controlled temperature and relative humidity (21°C and 65% humidity to prevent static from giving a false reading) for a minimum of three to five days. Then a small sample is taken, which varies between 20g, 30g or 1oz depending on the country. The down is then placed into a clear tube and agitated. A weight is then placed on to the down and allowed to settle.
The poorer, denser feathers will compact more than the finer, loftier feathers and so a measurement can be made to find the cubic inches per square ounce (i.e. 500, 600, 800 etc). The test is only accurate to within 5%, so your bag may not be quite as lofty as it appears unless the tag claims a minimum fill power. The problem is that because the size of the tube, a sample of down and lid weight vary from country to country; one man’s 800-fill will be another man’s 650-fill. The US test quoted by most US companies gives a result 4% higher than the traditional UK ‘Lorch’ test. Most serious outdoor down manufacturers do extensive in-house batch testing to make sure what they say on the swing tag is what’s stuffed in your bag. When it comes to synthetic bags the loft can only be judged by the brand of fibre used, and perhaps is a bit like naming the bird that produces the feathers.
The actual loft of the bag comes down to the type of construction – how this material is sewn together – and its thickness that counts. The problem with this is that whereas with down, where you can make a judgment on warmth based on fill power, fill weight, and temperature rating, with a synthetic bag you can only go by overall bag weight and temperature rating, neither of which is a good indicator of warmth.
Temperature ratings are a mess at the moment because although most manufacturers have ditched the confusing season system, not all of them seem to show if their alternative temperature ratings follow the new European EN 13537 standard, which leads to even more confusion. This standard roughly gives a comfort temperature rating, meaning the temperature at which an inexperienced user will feel comfortable (hot and cold), and an extreme rating at which an experienced user could use their clothing in order to stave off hypothermia!
The EU norm also shows a different scale for men and women, as a woman are generally colder sleepers due to differences in metabolisms. Never the less if you trawl the manufacturers’ web sites you’ll find a lot of different figures, with many just giving one minimum temperature, leaving you to guess if that means when the bag reaches that temperature you’ll be smiling or just barely alive! Whatever the figure lab-based test can’t be relied on in a real-world situation, and so should only be used as a guide.
Personally, I’ve never had a bag that lived up to its temperature rating, mainly because I suffer from cold feet meaning the guaranteed comfort zone doesn’t match with my feet’s idea of comfort. People have different metabolisms, some people are well fed while others are hungry, and some get into their bags warm while others start cold, all of which play a huge part in the actual warmth of the bag. Another big factor is how do you judge comfort?
For some, it’s not being cold, while for others it’s being hot. Experience is the best guide here, and if you haven’t got any then talk to a broad range of people who do what you do. As a broad guide here are some ideas on bag types:-
Down: 300 fill weight / Synthetic: 800-1000 grams total bag weight
Comfortable UK summer camping when naked. Marginal comfort (around freezing), with extra clothes on. Bearable – but not nice - below freezing for those well fed, well clothed and fit who use all the tricks in the book to boost the performance of the bag.
Down: 500 fill weight / Synthetic: 1200 – 1500 grams total bag weight
Comfortable for UK spring and autumn use naked when in a tent. Can be used in colder temperatures (-5° to -10°) when combined with clothes.
Down: 700 Fill Weight / Synthetic: 1700-2000 grams total weight
Comfortable for UK winter use naked inside a tent. Can be used in colder temperatures when combined with clothes (-10° to -15°).
Down: 1000 Fill Weight / Synthetic: 2500 – 3000 grams total weight
Comfortable high winter camping naked inside a tent. Can be used in colder temperatures when combined with clothing (-20° - 30°).
Note: If you suffer from a poor metabolism and feel you are a cold sleeper then pick a bag from the next category up. The quality of the down will also have an effect on the bags warmth, and the fill weights assume the bag is off between 600 and 800 fill power.
If using a down bag over a very long period in hostile conditions, meaning it will get damp, then you should try and make sure the bag has extra insulation. This means if you’re heading off on a five-day route and you assume your bag will lose 10% of its warmth each night due to it getting damp, you will have enough insulation at the end to keep you warm. This is one of the advantages of synthetics, in that if it’s OK at the start it’ll be OK at the end.
Weight is very important for anyone doing anything beyond car camping, and especially when it comes to climbing with your camping gear. It is here that the climber must make that difficult decision whether to sleep warmer but struggle with a heavy bag, or suffer a little and go lighter.
This choice can only be made based on the length of the climb, the weather, and the temperature to be expended, plus the amount of suffering you’ve already experienced! With gear getting increasingly lighter it’s now possible to save over a kilo here and there which is well worth ploughing into your sleeping system, as a good nights sleep will give you more energy than you would save by taking a cold bag.
Another important aspect is the increased psych you gain from knowing you will be warm when pushing on, and the reverse, of not wanting to push it knowing that you’ll suffer if you have to bivy. Compressibility is important if you want to use the smallest rucksack possible, but the difference in weight these days between a down and synthetic is marginal, especially when the down bag has picked up the weight of moisture after a few days. The bulk of a synthetic sleeping bag may mean taking up an extra 5 litres in your rucksack, but may pay dividends when your mates sleeping bag weights more when it’s wet yet doesn’t even keep him warm anymore.
When it comes to fabrics the main choice is how water-resistant – or waterproof, you want your bag to be. Basic models will feature a non-breathable nylon outer that will resist the odd spill but won’t survive a damp night without a bivy bag. Breathable water-resistant (often meaning waterproof but non taped) shells gives much greater insulation, and can even be used with a bivvy bag in quite damp conditions, and in the case of synthetics be used without a bivy bag in pretty miserable conditions.
Taped waterproof outers are now more common, offering a huge degree of protection, especially helpful if you’ve got a down bag. Last year I used such a bag for several nights bivvying on a face in the alps with a bivvy bag and was hugely impressed. Whether Shell you go for you must be prepared to pay, so its worth deciding whether you need the extra protection.
Not all bags are the same, with some being very roomy, while others are more form-fitting. A close-fitting bag weighing in at 1kg will be far warmer than a roomy bag at the same weight. This is because firstly there will be less convection, meaning less dead air to move around and be warmed, and because the same amount of down will be covering a smaller area. The main reason for going for a bigger bag is if you suffer from claustrophobia, or if you’re a bigger person! If you’re on the short side then try and buy a shorter bag, and companies like Rab or PHD will make you such a bag (and the same goes for if you’re the type of climber who has to listen to the words “but I can’t reach that hold!” from your partners).
If you’re an un-tall woman (sounds better than saying short), then there are also several women’s specific bags on the market that are both shorter and narrower, with some even having more insulation at the feet and upper torso. Alpinists and those who may have to sleep sitting in their bag should make sure this is doable, like most people when wearing a helmet, don’t fit into a bag when suffering in such a position.
A zip helps you cool of in the summer and allows two opposite sided bags to be zipped together for canoodling (make sure the person sleeping next to you agrees to this first), or to gain more warmth in a desperate bivy. Half zips or no zips only work for those bags that will only be used in the coldest places, and oh yes, it’s left-sided zip if your right-handed and visa-versa.
With sleeping bags, you get what you pay for, and you need to look at how many times you’ll use the bag and where when it comes to deciding what’s a fair price. If you pay £400 for an 800 fill power, Gore-Tex covered bag and it keeps you alive through five days of a storm on the Grandes Jorasses then you may feel that money was well spent, wear as your mate who bought a bag with the word “moon” stitched into its gossamer-thin fabric, may well find his £15 a poor purchase as he slips into a coma!