well, I didn't know this. but I had a mat that I had ironed on when I first started quilting. and yes it warped it. oh, like in 2005 just after I retired. anyway, I did not throw it away, because I had heard you could use it in the bottom of purses, or just turn it over. had it standing behind a shelving unit. I got it out the other day, and it was not warped anymore. wow. aging it, must have un-warped it.