The padded seat is made of high-resiliency molded urethane foam. The Ultra Seat option is 1/2" thicker than the thin seat option. The thinner option is very sleek but not the most comfortable. If clean lines are your thing, and comfort isn't, go for the Thin Seat Foam. If you work 8 hours a day in this chair and want it the most comfortable it can be, opt for the Ultra Seat Foam. If any of this is confusing, please reach out to our sales team at 888.467.6278, they know everything. Promise.