I finally got around to replace my old(!!!!!) mattress, and I got one of those memory foam ones that come compressed in a box. Wow, that was the weirdest thing I have ever unpacked. Out of the box, it was tightly rolled up in a plastic wrap. Before I even started cutting it open, I could hear a strange noise. It was air getting into the wrap, and the mattress already started expanding.
Once the plastic was off, it kept getting bigger like one of those tiny towels you have to soak in water. Within a few minutes, it had grown to full size.
Anyway, it's a wonderfully comfy mattress.