I can't imagine how that would matter. Probably just a marketing thing they are told to say to get you to buy a "matching" tempur pedic bed. Firmness is subjective, as is thickness. I sleep with my arm under the pillow with my head over my bicep, so I don't like a pillow that is too firm or thick. Someone that sleeps on their back on the other hand might prefer a firmer one molded to that position, such as some of the shaped pillows.I did stop at the tempur pedic store and the salesperson said choosing the pillow also depends on the firmness ( not not) of one's mattress.