R-value is how well an object resists heat transfer, or in easier terms, how insulated or warm it keeps you. Sleeping pads provide a barrier between your body and the ground, preventing your body heat from escaping and keeping you warm. R-value doesn't necessarily correlate to a particular temperature and is a stand-alone scale. A higher r-value means more insulation and a warm pad. 1-7 is a normal r-value range but some modern fancy pads inch towards double digits.