Twixt Ergo Desk Height Chair is designed to help support better posture & balance. Flexible ring under the 15" diameter seat allows you to adjust angle of sit (20 degrees) & provides movement for an active sitting experience. Height-adjustable stool features an upholstered seat & 360-degree swivel black base & cylinder. Height adjusts from 17-1/2" to 22-1/2". Aluminum base measures 14" diameter with TPU ring, steel piston & mechanism. The foam-cushioned seat offers a 2" thickness. Seat is also made with polypropylene, nylon fabric (mesh) & vinyl.