I don't know about inflatable mats but I am chipping in to say that when new my Multimat Superlite self-inflating mat came rolled very tightly and fitted into a plastic sleeve. After I had taken it out and looked at it I was completely unable to get it rolled up tight enough to get it back in the plastic sleeve. After several efforts I gave up, and the sleeve went in the bin.
Now, after a night's use, I open the vave (and would anyone would care to explain to me the purpose of its double valve, I have never understood that) and I roll it flat, if that makes sense, kneeling on each fold as I go to remove as much air as possible. The resulting flat roll fits nicely across my rucksack.
Regarding closed cell foam mats, I have heard of them being placed as a large tube in the rucksack, with everything else packed down the middle, though I don't know if anyone actually practices that.