>>643639>Because in the winter the air in inflatable mats still gets cold (especially on snow) so the foam insulates you from the cold air while still keeping you above the snowA ThermaRest type self inflating foam mattress has a foam core that provides the insulation and are as warm or warmer then a foam pad, whereas a conventional "hollow" air mattress will shut the heat out of your body in cold conditions, leaving you colder then if you had just slept on the ground.