The R-value, generally speaking, is a measure of the ability of a sleeping pad to resist heat transfer. Because a sleeping pad is such a vital part of your camping sleep system, it’s important to match your pad and sleeping bag for the overnight temperatures you’ll be anticipating.
The higher the R-value of your sleeping pad, the greater it will resist giving away your hard-earned body heat to the ground beneath it. R-values in backpacking pads typically range from 1 to 6, while camping mattresses are often warmer, and can sometimes reach double digits. For 3-season camping, consider a sleeping pad with an R-value of between 1 and 4, and for shoulder season or winter camping, you’ll want a pad with a value greater than 5.
It’s important to note that this rating system has only recently become standardized, and is now set in place by the international regulating agency ASTM International. This levels the playing field when it comes to comparing different sleeping pads.