When buying a sleep system it is important to consider the R-rating, referring to the thermal resistance of the product(s) and how that compares to the conditions that one will use them in. Some people layer two or more sleeping mats/pads in order to use them at lower temperatures than they are rated for individually. Is the cumulative R-rating of a layered sleep system a simple addition of the R-ratings of the respective layers or is the correlation non-linear.
For example if I have a sleeping mat with an R-rating of 2 and a sleeping pad with an R-rating of 4, if I place the pad on top of the mat do I get an R-rating of 6 (as in 2+4) ?
