The BackJoy Medical Line are seats that do much more than make you comfortable. It's a therapeutic seat that can help improve your posture, decrease peak pressures and maintain a lower temperature and moisture level at the skin. The BackJoy Medical line uses a pre-contoured top surface that promotes balanced posture. The bottom surface uses shorter pillars at the pelvis area allowing the cushion to dynamically contour under load. Made of durable closed cell EVA foam Meets CAL 117 requirements Utilizes innovative and patented port + pillar design Comfortable contoured surface Waterproof and heat-resistant up to 158F / 70C Breathable zippered cover that allows for free airflow Availability Comfort Tech 18"x18" (Large) 18 x 16" (Small) The bottom surface uses shorter pillars at the pelvis area allowing the cushion to dynamically contour under load. Ergo-Tech 18"x18" (Large) 18"x16" (Small) Shorter pillars at the pelvis area allowing the cushion to dynamically contour under load. Comfort Seat Comfort Seat - 15” x 15”x 1.5” Comfort Seat Plus- 18” x 16” x 1.5” Made of durable closed cell EVA foam Contoured surface. Utilizes innovative, and patented port + pillar design.