M Lightweight Inflatable Sleeping Airmats - State of the Market 2011
Part 1: Important Factors When Choosing an Airmat
by Roger Caffin and Will Rietveld
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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 grams (14 oz) for summer use and 800 grams (28 oz) for winter use. We will also look at the benefit gained by combining a very light airmat with a very light foam mat.
There is a surprising range of airmats meeting our criteria; 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 (individual reviews will come out with Part 2). The laboratory testing covered the insulation or R-value of the mats, and also the slipperiness. 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knew what they were doing - more than once we have seen quite ridiculous claims regarding R-values which were later withdrawn.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 matters too. It may be wonderfully thick and warm, but that is 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
- R-Value - A Brief Tutorial
- Practical Measurement of R-value
- Practical Requirements for R-value
- Field Assessment Details
- The Mats Tested
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Part 1: Important Factors When Choosing an Airmat"