I glued mine down to a piece of wood. Secure with clamps and weights (all over) until it dries.

Good luck

I cut one large one into different size mats. I use one for mouse pad, works great. I use one for the kitchen as a utility mat. It washes just fine. I like the idea of using the old mats for tote bottoms.

Using as tote inserts is a great idea.

I did the same thing. I used a piece of muslin to protect it and used my iron. Then I put it between the box spring and mattress for a few days. I can still cut on it but the ruler is off. Don't ask me how I know!

I would try setting it back out in the sun upside down and see if that will unwarp it

What size is it? I have turned on my oven to 250, shut it off, and put mat on cookie sheet for a few minutes. It worked, but it was not a HUGE mat.

My husband fixed mine. I had tried sitting it in the sun with heavy books on it, but I got creases where the books were. He said my mistake was putting several objects on it instead of one big flat thing.

So he set it in the sun, on the hot patio concrete and put a heavy piece of plywood type stuff on it. I forgot how long he left it there...at least several hours and maybe overnight.

It is fine now. I remember googling the problem and finding many solutions. You might try that also.

It might make good templates.

I had purchased a large one one time. I forgot where, it was shipped to me ROLLED UP!!! Can you belive that. I could not do anything with it. I called the company and they offered to send a new one. I said, I will shop else where, just give me a refund. They appologised up and down.
I ended up going to town and getting one in my local quilt shop!
I am a happy camper.
I have heard though, like the others, putting it out in the sun with something heavy on it. The gal that mentioned the ply wood sounds like a great idea.
Rememeber... No question is ever dumb!

Use it to make templates.