Warped self-healing cutting mat repair

 My self-healing cutting mat has warped. How do I flatten it?

You can flatten the mat by placing a couple of cookie sheets in the freezer until very cold. Place your cutting mat on the counter and put the frozen cookie sheets on top and weigh them down with something flat and heavy. Leave them in this position until the mat has flattened again for a few hours. This will usually solve the warping problem. Do not use heat to try to fix this, heat will do more damage.