The Truth about Sleeping Bags

[Since this article was written prices quoted have changed, but the general outline of the strengths and weaknesses of different types of sleeping bag has not.]

The 'truth'. Nothing like starting with a nice simple concept. A thing is either true or it isn't. Until of course you come in close and the pixels start to show. Then you realise that truth is usually built out of a number of bits which are half-true or hopefully true or some kind of true. Even with something as uncontentious as sleeping bags, truth comes qualified and conditional.

So let's begin a little closer to the ground and tackle something more specific, something we should be able to get some firm answers about. Value for Money.


'Value for Money'--The Questions

Sleeping bags are like other gear, we want value for money, a balance between price and performance. Price is clear enough, but performance? How good is the information we're given about bags: clarity or confusion? Are there any rules of thumb that can help? And do we really know what we mean by value for money anyway?

Go into any big outdoor shop for a sleeping bag and you're going to be faced with prices ranging from £25 to £400; and if the shop stocked an eiderdown bag, it would cost well over £1000. How can one bag possibly be rated 16 times (or 40 times) better than another? And all this without even talking about special items like GoreTex outers.

Of course you expect to pay more for more insulation. Four season bags cost more than their two or three season siblings. But why do we still find a six-fold price difference between bags rated the same (ignoring eiderdown)? Is the upper end of the price range being hiked artificially by a liberal dose of bullsh*t? Well, in fact you could say that the richest of the fertilisation is taking place among the cheaper bags. Let's put on the wellies of inquiry and take a closer look.

By the way, let's make it clear from the start that 'performance' in this section means just warmth / weight performance (the warmth you get for the weight you carry), with no esoteric extras like performance in the monsoon. This is a simple enough definition to allow us to come up with some answers straight away, isn't it?


The Standard Answer (via The Information Maze)

There's lots of info available, in catalogues, swing tickets, adverts and so on, enough surely to give us some real insight into the bags on offer. It's usually strongly presented and organised around three basic sections: fabric, filling and design.



Sleeping bag fabric is accessible. You can see it and feel it. If it has special properties, the information you get in the shop or from the catalogue is straightforward and (hopefully) substantially correct, and if its advantages are going to cost you extra, the choice being presented to you is usually clear enough. Such advantages usually lie in some degree of proofing, which can be very important indeed in certain circumstances, but which will do virtually nothing to add to the basic warmth of the bag. So with warmth / weight as the criterion of performance, little cause for confusion here. So far so good.



What about the second component, the filling, the 'meat' in the sandwich, where all the insulation is? You will also get plenty of information about this, the most important bit, but making a realistic judgement about it is much more difficult. True, you can see the thickness (as a guide to warmth) and you can feel the weight. But those stirring words in the catalogue or on the swing ticket about performance? Impressive? Try reading some of the others. They're all impressive. And the uncomfortable feeling may arise that you can't make a clear assessment here, that the information you're getting is too one-sided.

This battle of words is hottest among competing synthetic fibres, trying to raise themselves to the status of down. The words are backed up by scientific figures and graphs, and goodness, they're all so convincing. And isn't it amazing, they're all the best! And down bags are not far behind in marketing the superiority of their particular filling. 'Other companies use turkeys' feet, whereas we use only the finest bum-fluff from the Arctic goose harvested under the midwinter Moon . . . etc etc'. I'm not knocking the value of good fillings, just pointing out that the high-flown language is aimed more at influencing the customer than helping him to make up his own mind.

Now, loaded with the information about all these wonderful fillings, are you in a position to make a clear choice? Not really. Quite apart from the specialised nature of the claims being made, which are often difficult to invest with practical meaning, there are also at least two areas where promotion has erred into being positively unhelpful.

The first area of misleading information is the portrayal of synthetic fillings as virtually as efficient insulators as down. They are not. Some of them were hailed as reaching 90% of the weight / warmth efficiency of down years ago and they have been improved so often since then that they should now be outperforming down by a wide margin. There are indeed significant differences between some modem high quality fillings and their forebears. Their insulating properties are excellent - compared to other synthetics. However, on a straight comparison with down, their warmth / weight efficiency struggles to rise above 50%. So caution is advisable in reading some of that impressive blurb.

And second there is a curious anomaly in season gradings between down and synthetic bags. When their warmth is measured on a Tog tester (a machine which measures insulation), synthetics appear to have been given a rating about a full season higher than their down equivalents. A three season down bag often measures warmer than four season synthetic.

One can think of explanations. Synthetics are less likely to develop cold spots, they do not suffer as much when damp, and so on. But the main reason seems to be that it has always been done this way and no one in a competitive market can afford to step out of line. Downgrade your synthetic bags by a season and you'll look bad against all the other brands.

There's less of a problem with this of course if one is only comparing one synthetic bag against another - and as long as the customer understands the game. But does he?



That's enough about fillings for the moment, because the third basic component in sleeping bags needs a mention. Design. This is the trickiest of the three to comment on, and we're going to chicken out, having first justified our cowardice.

Everyone knows that good design can give a bag many genuinely useful features. Foot-pieces, mummy hoods, collars, zip draft tubes etc. Things which used to be special are now standard good design, used by most manufacturers. They are usually well described in publicity material and form almost a tick-list of value. The difficulty arises when considering extra design features which differ from brand to brand and for which conflicting claims are made (of course they're all the best).

For simplicity let's divide these extra features into two categories: those which enhance comfort or function, and those which directly affect the basic warmth / weight performance of the bag.

The first are so diverse it would be impossible to comment on them sensibly here: unique hoods, foot-pieces, zip baffle systems, and so on. By means of the second (for example the use of shingle construction or edge stitching in synthetics, and elastication or special baffle systems in down bags) it does appear possible to improve warmth / weight efficiency by 10% or so. This is a worthwhile difference when choosing between two similar bags, but it can be tricky for a buyer to evaluate, unless he already has experience of this particular feature.

So where does that leave you, faced with every brand claiming the ultimate design? On your own, mate. Us, we're not getting involved in this lengthy and contentious subject here; we're heading off towards some nice sweeping generalisations instead.

So now you know?

Now that we've looked briefly at the main kinds of information readily available to you, are they going to make the Value for Money questions any easier to answer? A little. But the deeper you go into the details, the more complicated it becomes, The problem is that there is too much information, much of it impossible to verify or evaluate, despite the simple EN classifications now being used.

So what can we do? In the circumstances the best way to come to something useful is often to be less ambitious, to reduce the scope of the inquiry to things which can be measured, and to see what information we can get from this more modest approach.

In what follows we've made the attempt to help in a simpler way, by drawing up some broad outlines about sleeping bag performance. It may remove some of the confusion and give you a firmer basis for choice. And if it's done nothing else, it's allowed us to indulge in some fun and games (called 'research' in scientific circles).

The Alternative Answer

Let's start at the beginning again. Like all simple concepts Value for Money is more complicated than it looks on the surface. Value is what you would like to be sure of when you buy, so it doesn't seem helpful to say that it depends on what you want. But you can really make things easier for yourself if you look at the main points formulated in the Tables below and ask yourself what you want, before you launch into the seductive tangle of swing tickets and technical information.

To make the basic points about value clear, we separated all the bags we've tested into four categories, based on the type of filling.

  1. Down: the downs in the tests were all high quality and the bags highly priced: eiderdown was also tested along the way, but has been left out of the figures as being too much of an oddity.
  2. High Quality Synthetic (HQS for short): top of the range fillings from leading brands: average price of bags tested was about £90.
  3. Cheap Synthetic (CS for short): low range or no-name fillings: average price of bags tested was about £55: 'cheap' means in terms of the specialist outdoor market.
  4. Feather & Down: (F&D for short): such bags are rare these days, but included as a joker.

These categories proved to be more than just arbitrary: they gave very homogeneous results, which remained remarkably consistent over a period of 20 years. The one result out of line with all the others was that the Cheap Synthetics actually offer more warmth for your money (Togs per £10) now than they did in 1990, while the other categories showed the adverse effect of rising prices. The figures quoted are averaged from the most recent results within each category, the only way to make them relevant when prices are involved.


1. Warmth for Money (at purchase)

First we looked at straightforward warmth: how many Togs do you get for £10? (Togs are a measure of insulation: more Togs more warmth). For many people who never intend to carry a sleeping bag more than five yards, this is a very straightforward measure of value for money. And there is a clear winner. The Cheap Synthetics are designed to deliver exactly this kind of value and they do. The only drawback is that synthetics do not stand well up to continued heavy usage (see Table 3), but why worry? These bags are relatively so cheap that you can just buy another when the first one dies.

Table 1 - Togs per £10
Cheap Synthetics (CS) 1.30
Feather & Down (F&D) .90
High Quality Synthetics (HQS) .75
Down .49


2. Warmth / Weight Performance

As soon as you start carrying your sleeping bag, the whole basis of value changes. Lightness - and to a lesser degree compressibility - now become as important as warmth and cost. And the longer and more difficult the trip the more imperative it becomes to save weight, until you reach a point where the risk of misery or failure as the result of carrying a heavy bag makes price by itself a poor criterion for choice.

Warmth for weight (Togs per Kg) now becomes the primary scale of value and the order of merit is dramatically reversed.

Table 2 - Togs per Kg
Down 9.80
High Quality Synthetics (HQS) 5.01
Feather & Down (F&D) 4.94
Cheap Synthetics (CS) 3.32


As we said earlier, down has no competition when warmth / weight is taken as the measure of performance. While F&D, which performs so well in several of our Tables, is shown in a different light: it is a comparatively heavy filling. The HQS bags, for all their claims, have increased their warmth / weight performance by only about 5% since 1990: they are improving, but major changes to Table 2 are not in sight.


3. Length of Life

Now it's time to introduce the final criterion into our Value for Money enquiry: length of life - that is, how long before your bag has deteriorated to the point where you are thinking about replacement.

Table 3 - Length of Life
Down 10 years
Feather & Down (F&D) 10 years
High Quality Synthetics (HQS) 4 years
Cheap Synthetics (CS) 4 years


Seeing that so much depends on the level of usage, these figures may seem arbitrary. And to some extent they are. Testing helps, but gives no definitive answers here. We have done long-run laboratory compression tests which have seriously degraded the loft of synthetic waddings, while the same tests have had virtually no effect on down. We have also stored both down and synthetic bags in small stuff sacs for up to 3 years, to see how they would recover after prolonged compression.

But none of these tests can reproduce the effects of actual usage, and it is from the accumulated experience of many users over thirty years that we come to these figures, stating them as a reasonable average. An average. Heavy use can seriously affect a synthetic bag within two years and down within five. On the other hand we have seen down bags in excellent condition after twenty years of regular use, and with moderate usage a synthetic can give you ten years' good service. And whatever the actual years of life ascribed to each filling, wide user experience tells us that to give natural fillings two and a half times the lifespan of synthetics is fair, if not a little understated.

Also, we have quoted the same lifespan for HQS and for CS. This is again a generalisation. HQS fillings usually contain finer denier fibres, giving them higher insulation figures and a softer hand. The downside to these fine fibres is that they tend to lose their loft more quickly than the thicker fibres used in the CS. With so many waddings on offer, many of them a blend of thin and thick fibres, this is already a complex subject without introducing the variations caused by different finishes. Suffice to say that in our experience the relative warmth offered by HQS and CS bags is likely to deteriorate at about the same rate.


4. Warmth for Money & Length of Life

Let's extend the scope of Table 1 'Warmth for Money' by connecting it to the figures in Table 3 'Length of Life'. How long is your bag going to keep giving you that great value you bought it for?


Table 4 - Togs per £10 x Length of Life

Feather & Down .90 Togs x 10 Yrs = 9.00
Down .49 Togs x 10 Yrs = 4.90
Cheap Synthetics (CS) 1.30 Togs x 4 Yrs = 5.20
High Quality Synthetics (HQS) .75 Togs x 4 Yrs = 3.00


You can see now why the army used Feather & Down Bags for so long - cheap and durable. Unfortunately, after a wet bivouac they weigh a ton!


5. Warmth / Weight Performance & Length of Life

If you want high technical performance year after year, look no further. There is only one filling worth looking at. Down states its real case here.


Table 5 - Togs per Kg x Length of Life

Down 9.80 Togs x 10 Yrs = 98.00
Feather & Down 4.94 Togs x 10 Yrs = 49.40
High Quality Synthetics 5.01 Togs x 4 Yrs = 20.04
Cheap Synthetics 3.32 Togs x 4 Yrs = 13.28


6. Grand Final Table of Everything Mixed Together!

Having come this far with the number games, it would be a pity not to finish it off and multiply everything together. Not as much use perhaps as a final table should be, because it mixes up such very different criteria for buying. But it does have something to say - and it's fun anyway.

Grand Final Table
Togs per £10 x Togs per Kg x Length of Life
Down .49 Togs x 9.80 Togs x 10 Yrs = 48.02
Feather & Down .90 Togs x 4.94 Togs x 10 Yrs = 44.46
Cheap Synthetics 1.30 Togs x 3.32 Togs x 4 Yrs = 17.20
High Quality Synthetics .75 Togs x 5.01 Togs x 4 Yrs = 15.03



That's as far as we can go with these figure games. Are they of any practical use? We feel that they are as long as, like all 'figures', they are not taken too seriously. (Did you notice we omitted to put Tables 1 & 2 together? Just testing to see if you're still with us. Actually it seemed a bit pointless; it would be another mishmash rather like Table 6.)

We know we ducked several key issues in the first half of the article, to say nothing of the ones we left out altogether; that is in the nature of all generalised comment, as well as being enforced by lack of space - we never set out to write a book. But there are no deliberate omissions which we feel would change the overall picture set out.

We also based the Tables on tests covering only a fraction of the sleeping bags on the market. We know that people will be tempted to weigh in from all sides with exceptions that do not agree with our figures. But we were struck by the consistency of the results over brand, design and time. It was this consistency which gave us the confidence to generalise.


Final advice on buying a bag?

Cast an eye over the Tables, make up your mind what you really want from your bag, then go and ask your friends - they're as likely to be right as anyone.

So whatever happened to 'The Truth about Sleeping Bags'? Well you see it's a complicated subject . . . maybe some other time.

The tests were usually blind, not based on brand, and looking for information rather than quotable results. No such tests are ever perfect or conclusive, but these were as fair as we could make them.

A Word for Synthetics

In case the reader thinks that we are making a case against synthetics, let us state the obvious. If you are going into a situation where your bag is likely to get really wet, don't take down. There was a test made some years ago in which a down bag was shown to dry out as fast and effectively as a synthetic. In a pig's eye! Saturate both, wring out the main water, and see what you have left. You could pass a reasonable night in the synthetic, which should give you around 50% of its full insulation. The down bag would remain a horrible flat lumpy mat, possibly for days, offering less than 10% of its original warmth.

This illustrates where figures such as these Tables can only give part of the story. High Quality Synthetics, which came last in the final Table, are the only real alternative to down for serious expeditions and in some cases may even be the best choice.


The figures in this article are based on Tog tests carried out, mostly at Leeds University, over a period of twenty years. Most tests were made on actual sleeping bags from many different brands. The other method used was to compare simple pads of different fillings enclosed in identical fabric. The general conclusions were borne out by both types of test.

High Quality Synthetics Tested

For the record a dozen different synthetic fillings featured in the HQS category over the whole period. From the bags we tested there appears to have been a small general improvement in weight / warmth performance: we measured about 5% in the last decade.