I've used them on 2 different cars, and if you are **** like myself when it comes to keeping a clean car, then they are fine. As a rule of thumb, when the car gets wet - take the bra off and let it dry overnight, and of course as mentioned clean out the underneath to aviod the trapped dirt problem. When you wash the car (driveway or car wash) remove the bra and clean/dry it separately. If you are lazy when it comes to cleaning - then a bra is not your solution.