This BackJoy Core (the one with the polyester fiber covering) tends to be more flexible than the Posture Plus model, and in general, it works better in a harder seat than a softer seat. The BackJoy Posture Plus (the one with a polyurethane covering) tends to retain its shape better and therefore works better in a cushioned chair. Determine which kind of seat you’ll be sitting in most of the time and choose the BackJoy that performs best under those conditions: you’ll get more of the intended effect. ..More