As a general rule, I would never fold the PVC mats. They will crack over time and you will be left with permanent creases in the vinyl. However, if you're just folding it up to chuck it in a bag, as long as it isn't pressed too tightly, you should get away with it.
The canvas mats are much more resilient and you can usually fold those as many times as you like. They will eventually take some damage, but only after a considerable amount of wear.