Guess I never thought about it - but I don't spray starch on my mat. I use my mat primarily for ironing my embroidery when it is done and shirts with buttons. When I am ironing large pieces of fabric I have my home-made ironing board. My wool mat is only 17 x 24.
If you have a large one used bought that was a horse pad - those are cleaned not sure how they do it - most likely spraying them - but they are cleaned.