My mat doesn't have memory foam, but synthetic insulation. There is also a built in pump so I don't have to breathe in the thing to get it firm. The pump works great, but I keep it a bit soft, especially in a hammock since I don't need it for padding, just insulation (obviously).

I also like that it folds down pretty dang small for backpacking.

Check it out... http://www.youtube.com/watch?v=Q61wnopqonA

and... http://www.youtube.com/watch?v=lpa9qNictSs