Here is an idea that has been passed around our quilt guild: Take your warped mat to Kinko's and have them put it through the machine press used (ordinarily) for attaching a poster to a posterboard. The machine heats to 200 degrees and draws a vacuum. Some one actually tried this and it worked and saved the cost of a new mat. Kinko's charged $8 for a large mat and $5 for a small one.