Tips for Buying an Outdoor Sleeping Pad
The task of insulating mats is to keep the cold of the ground away from the warm body. Because even the warmest sleeping bag cannot insulate downwards, as the filling is flattened with your body weight. In addition, a comfortable sleeping pad increases sleeping comfort and ensures more restful nights.
Sleeping pads are available in different thicknesses, lengths and widths. When choosing the length, please bear in mind that when you are lying on your back with your legs stretched out, your toes tip backwards and you are therefore longer than when you are standing. When choosing the width, it is advisable to take the width of your tent into account. Basically, the larger the mat, the more comfortable it is to sleep. But of course, the pack size and weight also increase with increasing size.
While comfort is very much subject to subjective preferences and cannot be measured, the ability to insulate can certainly be compared. This is done with the help of the standardized R value (heat transfer resistance), which (put simply) indicates how much resistance (hence the R) the mat can oppose to the passage of heat. All common information is in US units - which does not detract from the comparability. While not entirely correct from a physical perspective, the R-values of sleeping pads are commonly considered to be cumulative. That is, if you put two mats with an R-value of 2 on top of each other, the result is an R-value of 4.
The information given below about the suitability of mats only serves as a rough guide, as individual and environmental differences cannot be taken into account.
R value suitability
0 to +15°C: suitable for midsummer
1 to +7°C: for summer and mild spring and autumn nights
2 to +2°C: spring to autumn, without ground frost
3 to -5°C: suitable until mild winter
4 to -11°C: 4 seasons, suitable for winter
5 to -17°C: suitable for winter
6 to -24°C: suitable for winter, for high alpine tours
7 to -32°C: suitable for expeditions
8 to -38°C: for extreme expeditions
9 to -45°C: for extreme expeditions
10 to -50°C: for extreme expeditions
There are now three categories of sleeping pads: foam mats, (self-inflating) sleeping mats and thermal mats (also: insulating air mattresses)
Good mats in this category are made of closed-cell Evazote or polyethylene foam, which does not absorb water and is permanently pressure-resistant. The great advantage of these mats is that they still insulate even if, for example, a thorn or dog bite should have punctured the material. They are relatively light and cheap to buy, but a bit bulky. The insulation performance of mats of this type varies depending on the thickness and material from pure summer use to winter suitability.
Self-inflating sleeping pads
The main advantages of this further development are the smaller pack size and high sleeping comfort. The core of the mat consists of an open-cell polyurethane foam surrounded by an airtight and watertight shell that has one or more valves. Some mat cores have channels and/or punched holes in the material to reduce weight. When not in use, the mat is rolled up and the foam is compressed. If you open the valve, the elastic foam can follow its efforts to resume its original shape. Air is sucked into the foam. An additional supply of air is also possible by inflation and improves the cushioning effect.
Even thin mats of this type insulate enough to be able to sleep outside from spring to autumn. They only reach their limits in the double-digit minus range - not because the insulation performance of (thicker) mats is fundamentally insufficient, but rather because the final blowing up always brings moisture into the mat. This moisture threatens to freeze on very cold nights, which causes the foam to break at the latest when it is rolled up and thus reduces the insulation. Some mats can therefore be inflated with the help of a pump bag or similar, which prevents moist (breathing) air from penetrating. Self-inflating mats are quite robust, although ultra-light mats save on material and should therefore be treated with more care. Holes must be patched so that the mat can insulate well again.
Thermal mats / insulating air mattresses
The mats in this category are characterized by a high level of sleeping comfort and a minimal pack size. The thermal mats combine the principle of the well-known air mattresses with different types of insulation. The insulation can be based on cleverly designed, aluminum-coated partitions or, for example, on high-quality synthetic fiber or down fillings. All types have in common that the mats do not inflate themselves, but have to be inflated manually. This is done either with the help of an integrated pump, a pump bag or with the mouth. However, the latter also introduces humidity into the interior, which reduces the insulation. Mats in this group can be used all year round and even in deep winter - with the exception of a few ultra-light models, which are more suitable for more moderate outside temperatures.