I change out mats often. When I find a sale I buy one if I need it or not. I counted six big mats behind my bookcase and I know I have many smaller ones in drawer. I only buy when I find a 50% off sale. I always have a new one available. Once I get grooves in a mat I call it worn out The self healing mats will dry out. They need to be hydrated to stay self healing. Soak it in room temp water over night and let air dry flat, not in the sun. I do this with the new mats about once a year that I have in my stash and haven't used yet.