Sea to Summit has always tested its sleeping mats for R-Value in a laboratory; to date we have worked with the EMPA labs in Switzerland. Complete, production-quality mats are tested under laboratory conditions which include carefully monitored internal air pressure.
Because this level of testing was not followed by all sleeping pad manufacturers, REI and MEC (the leading retailers in the US and Canada respectively) formed a working group which brought all brands together to agree on a testing standard (under the direction of the ASTM standards organization). That standard will become effective on January 1, 2020. It will allow consumers to compare R-Values across all brands.
The tested R-Value of an air mat does decrease as the internal pressure decreases (The Ultralight was tested at a pressure equivalent to 0.7psi which resulted in the quoted R-Value of 3.3).
However, it is important to know that even with the coming ASTM R-Value standard, the test is a static test.
A sleeper moving around on a sleeping pad pushes air around inside the air-filled chambers, and this may result in warmth dissipating from the pad. The Air-Sprung Cell design is far less susceptible to this than many other designs.
In a hammock two additional factors have to be taken into consideration:
- the pad may well become ‘kinked’ in places due to the curved surface of the hammock, leading to potential loss of warmth (again, the Air Sprung Cell design is less susceptible to this) unless it is restrained in some way
- the pad may simply slide out from underneath the sleeper
I trust the above is helpful; please let me know if I can provide additional details (including how R-Values are tested).
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