The ErgoSit Seat Cushion makes you sit up straight while working your abs. The air-filled Ergo Sit Cushion is 14 inches across, and is an innovative way to improve posture and promote better balance. Sitting on it encourages upright posture, which means less stress on your spine. Strengthen your back and abdominal muscles while working at your computer or put it on the floor to exercise your legs and feet. Use the round side forward for active sitting. Use the straight edge forward for thigh support and more stable sitting. Also works great as a back cushion and lumbar support, comes already inflated to the correct amount for sitting.