To ensure that you will be warm when you sleep (especially when the ground is colder), it is essential to know how well your sleeping mat resists heat loss into the ground. This resistance is known as an R-Value.
A laboratory-tested R-Value is the only way to measure resistance to heat loss. Sea to Summit has always provided independent lab-tested R-Values for its sleeping mats.
Since January 2020 we have used the industry standard ASTM F3340-18 test to provide R-Values for our mats.
There are other factors which will determine how well a sleeping mat will insulate; but the standardized ASTM R-Value test means that you can compare resistance to heat loss in sleeping pads across different brands.