A method for use in an automobile includes the steps of: providing an inflatable device having a shell formed of an airtight, flexible and insulated material that is specifically sized and configured to fill a volume of space within a lower rear interior compartment of the automobile behind the front seats and below the level of a plane extending between the top of the front seats and a bottom edge of the rear window of the automobile; installing the inflatable device within the rear compartment of the automobile; inflating the device and causing the device to completely fill the lower rear interior compartment; reducing the interior air space within the automobile and preventing circulated air of the automobile's climate control system from circulating into the lower rear interior compartment, thereby improving the efficiency of the climate control system and fuel efficiency of the automobile.