Lightweight Inflatable Sleeping Airmats – State of the Market 2011
Part 1: Important Factors When Choosing an Airmat

Introduction

One thing we know for sure: sleeping directly on the ground is usually not a good idea. The ground can be very hard; it can be very cold. Why use an airmat instead of a slab of foam? There are two good reasons to prefer an airmat: it is thicker and more comfortable, and a good one has a higher insulation rating or R-value, to protect you from the cold underneath. But you don’t want to be carrying excess weight, so this survey is restricted to selected airmats weighing less than 400 g (14 oz) for summer use and 800 g (28 oz) for winter use. We will also look at the benefit to be gained from combining a very light airmat with a very light foam mat.

There is a surprising range of airmats meeting our criteria (see the photo above!); there are also many more mundane run-of-the-mill mats which are just too heavy and/or lack sufficient insulation value to be worth including. This survey will look at the selected airmats both in the field and in the lab. The full list of mats tested is found at the end of this article. The laboratory testing covered the insulation or R-value as well as the slipperiness of the mats. Both are a bit complex. For field use the authors tried the mats out under a range of conditions: things sometimes happen in the field which can take you by surprise.

It might be obvious that the R-value is relevant, but a reviewer’s life is not that simple. Sure, the manufacturers quote R-values for their mats, but they don’t specify the measurement conditions. In particular, the manufacturers do not specify how inflated the mat was, or how thick it was during the measurement process. Were they measuring an area at the foot of the mat, where it is usually at its full thickness, or at the squashed region under your hips? As you will soon see, the thickness of the mat does matter – so we measured the R-value under a range of ‘inflations’ or thicknesses. The results make us ask whether they knew what they were doing – more than once we have seen quite ridiculous claims regarding R-values which were later withdrawn.

While it is not normally a specification, the slipperiness of the mat does matter too. It may be wonderfully thick and warm, but that is of no use if it is so slippery that it slides out from under you when you turn over in the middle of the night. One thing that did come out of the field testing was that some mats do have the very bad habit of sliding out from under you! So, we also measured the slipperiness. This is a very poorly defined value, so we will go into how it was measured in some detail later.

It would be nice to be able to measure that mysterious parameter called ‘comfort.’ However, the nearest thing we could find was ‘thickness,’ so that will have to do for part of the job. For the other part, we took the mats into the field and slept on them. Hardly a scientific assessment, but it has some practical merit nonetheless.

Laboratory Assessment

First of all we need to decide what are the important factors in assessing an airmat – perhaps in some sort of priority list. Here are the authors’ ideas, but please don’t think that nothing else matters. In addition, we have essayed an over-all scoring for the mats, but please treat this with caution. It makes assumptions about priorities, and yours may differ from the authors’.

• R-value – if the bed you are lying on is cold, not much else matters. In this case, cold is cold. Us warm-blooded humans like to be (you guessed it) warm!
• Comfort – if the bed you are lying on is uncomfortable, most other things don’t matter much. But we recognise that comfort is hard to assess and can be a very personal thing. Thickness will be used as a partial guide to this, along with outline and/or width.
• Dimensions – length, width, and thickness. It was noticeable that some vendors seem to measure the width (in particular) when the mat is almost deflated. Inflation always reduces the width. In the case of mats with bigger outer tubes, we measured the height of the inner tubes since that is where you are sleeping.
• Weight – always a high priority at Backpacking Light, as it does matter.
• Stability – allied to comfort, but it includes things like the slipperiness of the mat under you and the shape of the tubes making up the airmat. Some mats leave you rolling off the sides too easily; others feature larger tubes at the edges to prevent this.
• Ease of inflation – some mats self-inflate, while other require sustained blowing from an exhausted walker whose head starts to spin. A recent development has been mats with down or synthetic insulation with in-built lightweight pumps. The pump means you are not blowing moisture into the down inside.
• Outline – the shape of the mat. Typically, some mats are rectangular, while others are tapered or mummy-shaped. We have two distinct needs here: the tapered mats are fractionally lighter, but they are a real pain for couples if they leave big gaps between them.
• Packed volume – a rather low priority item as it is weight (not volume) which really matters on your back. Also, we found that packed volume varies significantly, depending on how much effort was put into squeezing all the air out.
• Noise – not normally of concern to solo sleepers who can tolerate their own noises, but definitely of concern to couples when one wriggles more than the other.

R-Value – A Brief Tutorial

What is this R-value that you read about everywhere at Backpacking Light? It is a measure of thermal conductivity – or how fast your body heat drains away to the cold ground underneath. Technically it is the ratio of the temperature difference across an insulator to the flow of heat through the insulator, and there is a strict analogy to an electrical resistor (R=V/I). However, while SI or metric units are given as m²·C/W, it can also be expressed in imperial units of ft²·F·h/Btu. The numbers for imperial R-values are about six times those for metric R-values and they are only used for building insulation products in America. We will not mention imperial R-values again.

We decided to measure R-value properly, rather than rely on the manufacturers’ claims. The equipment shown here was developed specifically for this, and the background and theory has been published here at BPL. Typically it can measure R-values to about 0.1 units, although we don’t claim anything better than about 0.2 units, or slightly worse at the extremes. As you will see soon, any higher precision is simply not relevant for air mats.

What does this R-value mean, in practical terms? It is a measure of how much heat is leaking away through a mat when you have a temperature difference across the mat. Obviously, a small temperature difference means that you (the warm object on top of the mat) are going to end up fairly close to the temperature of the ground. That is rather sad if the ground is cold. But, a high R-value may help keep you nicely warm all night. On this score it is worth noting that we have often heard novices complain of being cold despite having a very warm quilt or sleeping bag over them. Yep: the real problem was an inadequate mat underneath.

Note that we are talking here about the temperature difference across the whole mat. We are not talking about the thickness of the mat. Using closed cell foam as a simple example, you could easily imagine that a slab 50 mm (~2 in) thick is going to be a lot warmer than a slab 12 mm (~0.5 in) thick. We would expect the thick mat to have an R-value about four times that of the thin mat, simply due to the thickness. Now this may be obvious, but it does have some very important ramifications which we now examine.

What happens to the R-value when you squash a mat? More importantly, what happens to the R-value of that thin area under your hips while you are sleeping on your side? In general, the thinner the mat, the lower the R-value, subject to many caveats of course. So how do you properly assess the R-value of a mat? Do you blow it up hard and measure it while it is at its maximum thickness, or do you allow it to deflate down to a thickness all over you would expect to find just under your hips? When a manufacturer quotes an R-value for their mats, under what conditions does their specification apply?

We have here the data for the POE Ether Elite 6 mat from our recent review of it. When the mat is fully inflated (44 mm thick) the R-value can be as high as 4.5, but when the mat is squashed down to between 14 and 18 mm thick (as it might be under your hips) the R-value is only about 2.0. That’s a big difference! In fact, the manufacturer’s web site quotes an R-value of 2.0 ~ 4.0, which turns out to be a good description. Moral: beware of R-values quoted without any mention of conditions.

Practical Measurement of R-value

Just quoting an R-value for a mat does not tell you nearly as much as you need to know. It does not tell you under what conditions the R-value was measured, nor what area of mat was used, nor at what thickness. We are not going to go into that in any detail here, as the technical details have been fully published in our article on the Thermal Insulation Measurement System. Suffice to say that we measure the R-value over a reasonable area of the mat, and at varying mat thicknesses, and we will be presenting the full R-value versus thickness curves. The preceding two photos illustrate this.

There are some other limitations to measured R-values. In particular we have the issue of ‘settling time.’ It can take quite a while for the measured R-value to stabilise after a change: does this tell us anything about transient effects in the field? Fortunately the answer is ‘no’ – and that is based mainly on field experience rather than laboratory testing. Apart from the sad experience of a mat deflating in the middle of the night, or slipping out from under the sleeper, we have not noticed significant changes in the insulation value over time. But be warned: if you get moisture from your breath inside a down air mat, then you will notice a difference. Soggy down is not good.

While the thickness of the mat does affect the R-value, it also affects the comfort of the mat. Blow a mat up hard to get maximum R-value, and you will find it can be quite uncomfortable to sleep on. Let a bit of air out: the mat starts to mold itself to your body and comfort increases. We can’t tell you how much to let your mat deflate: it will depend very much on the shape of your body and your weight.

Practical Requirements for R-value

An obvious question is: what R-value do you need for summer and what is required for winter? There is no fixed answer to this; it will depend on such factors as:

• What you ate for dinner: no food means no energy and no warmth.
• How sheltered you are from the wind: even breezes steal a lot of heat.
• What sort of bag or quilt you have: a warm top cover can help compensate for a poor mat, a little bit.
• What sort of ground you are sleeping on: hard ground under your hips will compress the mat more.
• Who you have sleeping next to you: a snuggling partner is a wonderful hot water bottle.
• How warm the ground was when you put your mat down.

We could go further, but you get the idea. At the peak of summer, you could probably sleep on warm sand with no mat at all (been there, done that), although sand does get very hard around 2:00 AM. A thin mat with an R-value of more than 1 might handle most ‘nice’ or warm summer conditions. The rest might be more a matter of comfort anyhow: how thick a mat do you want?

However, come winter and the situation changes. The ground is going to be cold, especially if you are camping on snow. But snow is funny stuff: it can almost be ‘warm’ under some conditions. Heat will leak downwards through the mat and warm the snow up. Snow is usually a poor heat conductor, so it is quite possible that the snow directly under you may be around 0 C (32 F) for much of the night. What’s more, there will be more heat leaking through the thinner parts of the mat, like where it is most compressed under your hips. This means that the snow will melt more under your hips, and eventually give you a nice ‘hip hole.’ That means more comfort, but it also means more warmth. How so? Well, when the snow under the pressure points melts and sags a bit, the mat will tend to even out under you. The more even the mat, the better it will insulate at the critical places. Many is the time that what was a flat snow platform in the evening, has turned into a seriously contoured site by the morning! And thus, we slept well.

If you must have an answer for a winter mat, a minimum R-value of 5 would be a good starting point. Below that and you may have some problems, depending on how you sleep and other conditions as outlined above. A mat with an R-value above 6 should be fairly reliable, even comfortable. Note that what a mat offers does seriously depend on how thick it is in the field, and this is a major topic for Part 2.

Slipperiness

Perhaps it has never happened to you, but it has certainly happened to the authors and their wives: mats seemed to slide out from under us in the middle of the night, leaving us on the ground. OK, on one occasion the site was poorly chosen and tilted sideways, which is never good, but the problem has not been an isolated one. So we decided to see how slippery the different mats were.

Before one can measure something vague like ‘slipperiness,’ one has to convert the term into a concrete bit of physics. It was decided that measuring how easily the mat slid across silnylon when it had a weight on it would be a good idea – and one which could be measured. The one other requirement was that the sliding be done at a fixed and reasonable rate. The result was the equipment shown here.

Going from left to right, we have the following. There is the air mat under test, sitting on a layer of silnylon which is anchored out of sight to the left. That silnylon is sitting on a long airmat which is meant to approximate a soft bit of ground. It also smoothes out the small ripples in the wooden deck underneath – the smoothing turned out to be essential. On top of the airmat we have a square plate of timber wrapped in black plastic, and on top of that we have a calibrated mass (OK, two standard house bricks). The area of the plate was 430 x 355 mm (17 x 14 in), and the total mass of bricks and plate was 8.42 kg (18.6 lb). The leading edge of the mat is gripped by two soft-jawed clamps with attached cord. At the extreme right, out of the photo, is a fixed speed motor-gearbox combination with a winch drum. The cord around the winch drum goes to a small pulley and back to the winch, giving a 2:1 speed reduction between the winch and the mat. The forces involved were such that winch loading was not an issue. The result was that the winch pulled the mat along at a (fairly) uniform sliding speed of about 55 mm (2.2  in) per second.

In between the mat and the winch pulley is a calibrated spring balance. That’s what Roger is looking at carefully. It measures the actual drag force transmitted to the mat. Roger’s other hand is hovering over the power switch for the winch.

We have a couple of caveats about this measurement. We said the speed was ‘fairly’ uniform. That is because a couple of the mats tended to move in a rather jerky fashion: what we call ‘stick/slip’ movement. We were able to minimise this by careful attention to the layout, but it did happen. The other ‘problem’ which could be raised is that a load of 8.42 kg (18.6 lb) spread over the area of the plate is a lot less pressure than a sleeper would exert. This is true of course, but fortunately distributed friction is usually a linear function of the load – which means that doubling the load or pressure would simply double the drag force. We chose this load because it fitted nicely into the range of the calibrated spring balance we had. What is really important is that the relative rankings of the mats should generally be independent of the load.

Every mat was given several test runs to make sure that the results seemed stable. Only stable results were recorded. Also, every mat was tested both the right way up and also upside down. Many mats have different colours and textures (or fabrics) on top and bottom, so we wanted to see which side was more ‘sticky’ to the silnylon floor. Finally, a couple of the mats had been given silicone sealant stripes on the underside to improve their grip on the tent floor. We are able to see the effect of these stripes by comparing the results for right-way-up and upside-down.

We must make an important point here. The actual numerical values obtained from this test have very little meaning on their own. Do not attempt to compare them with anyone else’s values. All that matters will be the relative rankings between the mats. Finally, two operational details. For the first complete run the base mat was a Nemo Zor mat – a smooth one. For the second complete test the base mat was a NeoAir mat; that has cross-wise tubes. The results with the Nemo Zor mat as a base were about 10% higher than with the NeoAir mat as a base; the results with the NeoAir mat are shown. Second, some mats tested had a flat or smooth surface, while others used tubes. The flat mats are fine: they can be tested in any direction. The ones with lengthwise tubes are tested with the mat being pulled parallel to the tubes, and they run across the tubes of the NeoAir base. The NeoAir mat shown in the photo above was eventually turned at right angles to get sensible results, to point its tubes in the direction of pull. When tested as shown the drag force tended to jerk a bit on the Nemo Zor mat, and it bounced wildly over the NeoAir base. In the latter cases, the tubes of the NeoAir mat under test were bouncing over the tubes on the NeoAir base mat. It was, you might say, a bit of a ‘Duh’ moment!

Field Assessment Details

No laboratory testing can replace a good bit of field testing. All the mats were taken out in the field and slept on. In many cases the testing was shared with the authors’ wives – both Sue and Janet were roped in for this. It should be noted that couples sleeping together, especially in the cold, have a special requirement (or advantage) which does not apply to singles. One can keep the mats tightly together with tape loops; a few companies even sell such loops or offer means of connecting mats. Doing so helps stabilise the mats against wriggles: it is likely that only one person will be wriggling at a time. But that is not all. Keeping the mats together like that also allows us to snuggle up together and share warmth. Without the tape loops the mats tend to slide outwards or apart, leaving us on the (cold) ground in the middle. You might not care on warm pine duff, but you will care when camping on snow!

This issue of sleeping together is not a trivial matter, as sharing warmth has huge consequences for pack weight. There have been some autumn nights in the Australian Alps when all Roger and Sue had were thermals, two 550-gram quilts and two BPL Cocoon Jackets. It fell to -7 C (19 F) one night (a hard frost in the photo), and snowed significantly another night – but we were warm enough. The photos here show the mornings after. (In case you are wondering, I can only say that such variable weather is quite common in our Alps.) How did we stay warm? We used several good tricks. We taped the two mats close together so we were able to snuggle very closely. Because we were so close together, we were able to layer one quilt on top of the other and to spread them over both of us. That converted a 550-gram quilt each into a 1100-gram quilt with a large perpetual hot water bottle next to each of us! Without those tape loops, and mats which do not slide around, it could have been a very cold night. The moral here is that you should not think about your mat and your quilt separately: they need to be integrated. On which score, check out our review of the Katabatic Sawatch quilt, which specialises in such integration.

The second moral of the story is that the shape of the mat matters. Serious winter mats are heavier than light summer mats, but you should resist the temptation to shave off every corner of the mat in winter. One silly problem we did find for couples was the gaps at the head and foot ends left by mummy-shaped mats. In the photo here, showing a Mammut Down 7 Pump sort-of-mummy-shape mat next to a Big Agnes Insulated Air Core mummy-shaped mat, the gap below the waist level is very obvious. You can fill the gap with food or gear, but that may not be as comfortable. Mummy-shape may be fine for singles, but couples should think again.

So what we looked for during field testing was ‘comfort,’ ease of inflation, slipperiness, surface noise, and insulation. Most of these things tend to be subjective. Not all of these are listed in the basic fact table below as they need to be assessed. That has to wait until Part 2.

The Mats Tested

In this, Part 1 of the series, we list all the mats with the manufacturers’ major specifications. Our simple measurements (length, width, etc) are beneath the manufacturer’s claims where appropriate. In particular, note that the R-value quoted is the manufacturer’s claim. There is a reference to footnote for any extra details, such as when our basic measurement deviated significantly from the manufacturer’s claim. The order used is basically alphabetical and short-to-long, with some foam mats at the end. The foam mats were only tested in conjunction with (on top of) other mats. The rationale here is that a thin layer of foam plus an air-core mat might be as warm as a foam-core mat but end up lighter. In Part 2 we will give detailed discussions of every mat and list the specialised measurements we made.

Some of the entries lack a brand and a price, and that needs explaining. Some manufacturers make a mat in one size and that’s it, but other manufacturers often make a model in several lengths. Typically these might have labels such as Short, 3/4, Medium, Regular, Long, etc (S, M, R, L). Which length you choose depends on what you are doing and what weight-sensitivity you have. Out of interest, where we have tested one or two lengths for a model but other lengths exist, we have sometimes included one of the other lengths, listing only the manufacturer information but omitting the brand and price. In a few cases the one ‘model’ comes in both Rectangular and Mummy (R, M) shapes, so we have included a few of those as well. That does not mean we have included every possible shape and size for that model: no way. Check the Mini-Reviews accessible from Part 2 for more details of what was tested. But at least you know to look for the different shapes and sizes in these cases.

We should mention in the above context that our spot checks have shown that where a model comes in several lengths, all the lengths do share some common parameters, such as width, thickness, R-value and slipperiness. So you can do some extrapolation of measured data.

We will make a special mention here about the quoted prices. In most cases the price shown comes directly from the manufacturer’s web site. However, a few companies managed to be mildly to extremely frustrating about pricing, telling the customer to contact a dealer. In those cases a lot of searching was need to find a dealer who actually had stock; in one case a search of more than six listed dealers did not find one which stocked the mat being sought. While Backpacking Light does not have an official position about this, at least one author was sufficiently frustrated by this commercially suicidal attitude that … I give up. Guys, it’s 2011, not 1911! Grow up!

Notes

• * If a repair kit was supplied, there is an asterisk after the manufacturer weight. In the case of the Therm-a-Rest mats, a repair kit is available but it is an extra cost.
• The model name may be followed by an ‘M’ or an ‘R,’ for Mummy or Rectangular shape, where relevant.
• The class column covers traditional foam core self-inflating; air-core with an insulating layer (down or synthetic); air-core with internal baffles and air with no added insulation.
• Some mats are basically rectangular while others are mummy-shaped. For the latter, the width measurement is usually at the widest part.
• Length and width values were measured with the mat fully inflated. This decreases the width over the uninflated value of course, and some vendors seem to have quoted the uninflated width.
• Thickness values are especially problematic: how hard should one inflate and what load should one apply for the measurement? We inflated to a ‘firm’ state and measured from ground to a light metre (yard) stick lying on the top of the mat. In many cases this gives a bigger result than the claim.
• We have listed the claimed R-values here where available: our measurements will appear in Part 2.
• The weight listed is from the manufacturer; in general there is no indication whether the listed weight includes the supplied stuff sack or (in some cases) the supplied repair kit. The BPL weight is for the mat only.
• Some mats are self-inflating, some need to be blown up, and a few included in-built pumps.

Footnotes

1. Tapered mummy, all tubes same height, Primaloft layer inside top surface.
2. Clear PU film, looks like pool toy.
3. Classic Down Air Mat or DAM, short version. Longer ones exceeded weight limits, but could be considered for winter use. Outer tubes bigger than middle ones to prevent rolling off. Thick open-cell foam strip across end away from pump. Pump is two hands long. Slow deflation. Extremely difficult to find dealer with this mat.
4. This is a very strange animal. The width is nothing like the claimed value. Best wait for the Part 2 discussion. There is a also a slightly more conventional model recently released, but it is over our weight limit for three-season mats.
5. A range of mats were supplied to Will and Roger. Will got the empty LuxLites, while Roger got one with synthetic fill and one with down fill.
6. A very small tapered prototype design with outer tubes wider than middle tubes, since named the TaperLite. The width is at the wide end, the thickness is for the middle tubes.
7. Sort of tapered, but with rectangular cut-outs (see second and fifth photos). The internal pump is about one hand long and slow. Fast deflation. The outer tubes are larger than the inner tubes.
8. Basic simple rectangular foam-core mat, but with no coring or cut-outs.
9. Zor series released at Winter OR 2011 and not yet listed on website.
10. This model mat was recently reviewed here. It may now be superseded by the Peak Elite AC, which is very similar but includes a so-called ‘radiant barrier.’
11. Mummy mat supposedly containing Aerogel as well as foam.
12. This is an obsolete product, but it has served the author and his wife extremely well since it was bought in 1996, including many cold snow trips. It is here mainly for reference, to show what is possible. The ‘LE’ stands for ‘Limited Edition.’
13. The ProLite was reviewed recently here in the Small size. At that stage it was called a ProLite 3, but the name has since changed slightly.
14. The NeoAir was reviewed at its release in 2009, but the review was based on a pre-production version which had numerous faults. We did not know it was a pre-production version at the time! One has to ask why someone would send us a known-wrong sample to be reviewed.
15. Listed on website, but with no real details.
16. The Gossamer Gear Thinlite Evazote foam is a closed cell foam made with nitrogen as the inflation gas. It is probably close to an EVA30 foam. While not thick enough for ‘comfort’ use, it does have good insulation properties. The weight of two such mats differed a bit, so the weight of the more recent version has been used.
17. The ‘generic foam’ is good EVA30 foam (bought from a bulk foam supplier) with one small difference: It comes from the surface of a huge block of foam so it has a skin on it. This skin is extremely resistant to dirt and getting damp. However, the skin does add a bit of mass to the foam. How much you pay for such a mat depends on where you buy it. Cheaper versions are usually available in supermarkets etc, using a cheaper form of foam.
18. Stephensons do not seem to have any model name for their down air mat other than DAM. The specifications are very basic. Inflation is basically ‘blow,’ but they provide a large stuff sack which serves as a sort of pump, to keep breath vapour out of the down. The weight of this pump sack has been included in the weight of the mat.
19. While branded Backpacking Light, this mat is actually made for BPL by POE. There are two width measurements: one for each end of this very tapered mat. According to the (now defunct) BPL gear shop page, the weight of this mat has varied over a bit of a range, as indicated. Backpacking Light policy is to not review our own products, so this mat is included here for reference only.

Disclosure: The manufacturers provided these products to the author and/or Backpacking Light at no charge, and they are owned by the author/BPL. The author/Backpacking Light has no obligation to review these products under the terms of this agreement.