I change it when I get totally sick and tired of it! My ironing board is 50 years old, heavy, metal, clunky and the drop edge is almost 3". But it is really sturdy. It used to collapse, but it refuses to slide anymore, so it stays up all the time. Unfortunately, because of that, it has to now stay in the basement. Upside is I get my exercise running up and down the steps to iron the bigger pieces. Because of its size, I've never found a replacement that will fit, so I make them. I too put it back on when damp for a nice tight fit.