R-value

R-value measures how well a sleeping pad resists heat loss downward, using a lab test standardized under ASTM F3340 that most major pad brands now report on the same scale. A higher R-value means less heat escapes through the pad into whatever is underneath, whether that is soil, a tent floor, or a vehicle's cargo area.

Car campers often assume a metal or plastic cargo floor is warmer than bare ground, but it can pull heat just as fast, especially with an air gap or cold undercarriage below. Stacking two pads, such as a closed-cell foam pad under an inflatable one, adds their R-values together and is a common way to reach winter-capable insulation without buying one expensive pad.

When buying, match R-value to your coldest expected night rather than the mildest one, since an underinsulated pad is often the real reason a sleeping bag with a good comfort rating still feels cold. A frequent mistake is judging a pad by thickness or price alone, since a thick pad with poor insulating fill can perform worse than a thin one built for cold weather.