A sleeping mat odyssey

In 2001, EXPED introduced a revolutionary product - the DownMat – which created an entirely new category of sleeping mats – much warmer, lighter and more compact than previous mats. This new category necessitated a means of measuring and comparing the efficiency of the insulation, so we pioneered the use of R-value testing to determine the “warmth” of a sleeping mat. Almost 20 years later the outdoor gear companies have agreed upon an international standard method for testing the R-value of sleeping mats, based heavily on EXPED’s previous work with EMPA, the Swiss Federal Laboratories for Materials Science and Technology.

Let’s define what R-value is and why it’s important. First, R-value is a measure of thermal resistance (that’s the “R” part). When you buy insulation for your house, its efficiency has been tested and is expressed with a number: R-value. This allows insulation to be easily compared. The higher the number, the more efficient it is at retaining heat. R-value is a useful way to compare the insulation efficiency of different materials. In 2002 Andi contacted the Swiss Federal Laboratories for Materials Science and Technology. At EMPA, they had a device for measuring thermal resistance according to an esoteric German standard that turned out to be perfect for benchmarking the thermal resistance of sleeping mats.

In 2001, way back before ASTM standards, when we got our results by mail (with a friendly Swiss German “Salü”) our first test result for the DownMat was R9.5. In the end we adjusted the down fill for our target R-value of R8. 20 years later, in another lab, we get almost the same result!

Since EXPED’s first R-value test, many more brands have developed insulated sleeping mats, and it was clear that some kind of standard test was needed to make it easier for people to choose sleeping mats. Some brands did their own testing, some used EMPA and some simply made it up!

In the test, the mattress is pressed between two special measuring plates, one mimicking the cold ground and the other a warm human body. What’s left to define are a few parameters like mattress inflation pressure, pressure exerted by the top plate and number of samples to test.

To clarify, the new standard only defines how to measure R-value, not the temperature at which it should be used in the outdoors. The standard also doesn’t define where to test – but Exped has always tested independently and we feel strongly that this is the only way to eliminate the otherwise inevitable sales and marketing bias that prefers higher numbers over lower ones.

In conclusion, the new ASTM F3340 standard is a huge leap forward for folks buying and sleeping on sleeping mats. EXPED is proud to have played a lead role in its development and we look forward to improving the outdoor sleep experience for another 20 years.