I have no flip king size Stearns and Foster with somewhat of a firm pillowtop. The mattress was the best for about 2 years but then the pillowtop started to break down with depressions where we usually slept. The mattress underneath seemed fine. We called warranty and they came out and measured the depressions with no weight on the mattress. Of course, the foam of the pillowtop held up air just fine, it just didn’t hold up people! I don’t know if they still make mattresses that you are not supposed to flip, but if they do, I would not recommend them.