No. Depending on the flex additive you use most will evaporate out of the paint within a week or so. They are meant more for installing the parts so you can flex them around. Once they are on and installed they don't flex much at all really. I have painted two bikes now and didn't use flex in either one. Not really needed. Especially when using high quality paint/clear. They are decently flexible to begin with.

 

Sweet nice to know that. I didn't use any for my car than again car bumpers don't really flex as much as the panels of a bike when putting on and taking off.

 

You dont really need to if you're using acrylic urethane, you can ball that **** up and it wont chip