I clean it well before using. Another thing I always do is to put the old back into the package of the new one and write on it: Used. I keep it. If there is something non fabric to cut, like paper, cardboard, and in one case a piece of screen when we had to change the screen on the screen door, I bring it out and use it. I put it back into the package and discard it. Is amazing how many times the kids need to use a rotary cutter. I wonder what they did before I quilted.