When the cutting mats first came out, we all learned the hard way that you can’t keep your mats in a sunny window or the car because it would warp. Mine warped as I was traveling to an out-of-town class, what a disappointment!
Since only half the mat was really bad, I cut the mat in half and use the good side by my sewing machine at home. The warped side I turned it into a small cutting mat on one side and an ironing board one the other by gluing the mat down on a piece of plywood with some really strong glue. I keep this with my traveling sewing machine. I made it over twenty years ago now and it is still in use. I like mine way better than the commercial ones out there.
I also had two pieces of plywood cut a little bit bigger than my large cutting mat for when I want to take a larger mat to class. I bought four EXTRA LARGE black binder clips and put one on each side of the two pieces of wood (with the cutting mat in between the boards). I’ve kept this board in my car during the hottest summer days and it hasn’t warped yet. The boards keep it flat and safe no matter how hot it gets in the car.