I've been told that you can place your mat on a rack in the oven on very low heat for 30 minutes, then remove from the oven and lay it on a flat surface to cool. If the mat is not badly warped, I've had good luck placing it flat on my dryer top and placing a load of hot towels from the dryer on top of it.
I did a search for fixing warped mats, and most of them suggest that you use heat and pressure.
You could lay it out on your driveway in the sun with something on top of it for pressure, and to keep it flat. Depending on how warped it is, it may take some time to get it to lay flat again.
Or use your iron, cover the mat with a couple of layers of towels, and iron (low temp) over the warped area, applying pressure to the worst areas.
If you can not get the warp to go away, you can always cut it into smaller mats to ues near your machine, or to take to classes.
I wonder if that will fix a warped one? I didn't know not to leave one in the car...hot FL sunshine....when I first started quilting a few years ago. I've kept it...so maybe will try this. Not til next week though...going on a quilt retreat Fri Sat and Sun!!! Sandi in FL
Oh my Goodness this tip really works!!
I learned this tip from my guild retreat last weekend. If you have an "Olfa" green self-healing cutting mat(with out the padded ioroning surface on the backside)...you can restore it's orignal "cushie" & quick healing feature by "Rehydrating" it.
*Run the bathtub with about 2" of WARM water...more if your mat is super big.
*Slip the mat in the water completly, you might have to weigh it down, I used Shampoo bottles.
*Let it soak for about an hour.
*Take the mat out and dry completely. It's ready to use again.
Voila!! Restored mat...I can't believe the difference! I have several mats so I tried the cut "test drive", much easier to cut! I think that my blades will last longer, since I'm not pushing so hard on my mats and dulling the blades.
Disclaimer...I can't speak for any other cutting mats since I only have the Green Olfa mats. I don't think it will hurt any other brands of self-healing mats...but, I haven't tried it.
One other tip...flip the mat over use the back-side of the mat! It's a brand new surface! I used a permenent fine point "Sharpie" to make a new grid...I just extended the life of my mat!
Blessings!! Debbie S.
Longview, Washington USA
"If you are very patient...you will get into trouble slower."