What is the difference between memory foam pillows?

I was at target looking at memory foam pillows and they had three different kinds regular, deluxe, and supreme. All 3 pillows are 100% polyurethane foam, yet the supreme feels more high quality than the regular and the deluxe feels more high quality than the supreme. So what is the difference?
Update: What I mean is, how can all 3 pillows be 100% polyurethane yet one is cleary better than the other 2?
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