Tri-Flex seat cushion features built-in sitz bone contours and a waterfall edge for plush support that may help reduce pressure points during extended seating periods. Its ergonomic design supports leaning posture to further help minimize pressure on your spine and connecting muscles. Interchangeable seat cushion can be easily removed and replaced for variety or to fit your office decor. Seat cushion is designed for use with Mobis II and Pivot bases (each sold separately).