Mirra's TriFlex back provides flexible and continuous support while providing airflow. An additional adjustable lumbar support is available if desired. Should you opt for the lumbar support, pat yourself on the back. This is (in our humble opinion) one of the best functioning lumbar supports out there. It moves up and down, and also can be more passive or active by turning the lever on either side of the support that push into or rest away from your back.