My Olfa cutting mat got warped when my dearest love threw it willy-nilly into the back of his car when we were moving.
I laid it out on top of my car in the heat and within a few hours, it was flat as a pancake.
HOWEVER!!! The measurements were all wrong. If I followed the grid when cutting, I got wavy, wonky lines. I got sick and tired of having to measure everything with a yardstick and just bought a new mat.