Comfort seats have an articulating back rest. ie: the backrest is "hinged", which allows it to be adjusted to conform to the bend in your back. Comfort seats also have power adjustable head rests. The only downside to comfort seats, is that BMW uses the exact same bottom cushion as is used on the stock seats. imho, BMW "cheaped out" on the X5 comfort seat option by not using sport seat bottom cushions, which have additional side bolsters, and have additional thigh support.