[Perfectlap]

well you have to reapply raggtopp protectant after each use of the Raggtopp cleanser so assuming you wash the softop a couple of times a year....
During the summer when there is little rain fall and lots of dust several cleanings would be smart. Definitely if you get bird bombs or tree sap on there.
But dust is the big culprit, not so much winter. When dirt and debris get in between those fibers is when the break down of the canvas begins. Another reason why you should never get car wash soap on there, detergents attract dust. a weekly rinsing with a stiff stream is a good idea during summer.