I just used this folding gymnastics mat. I cut off one third of it, so it's only two panels. I thought I would need two of these stacked to make 4" platform but it turns out that one 2" is perfectly comfortable. Folds up in half when I'm not using it.
I did shorten one of the panels by a few inches (cut it open, cut the foam, the re-sewed it...no I don't know how to sew, but it was easy) so that it fits perfectly when folded open.
I've got a nice, high R value, Exped megamat that I unroll on top of it.
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