I drive with my window down alot and have noticed that the headliner on my driver's side looks a bit darker and dirtier than it does on my passenger's side. I'm guessing it's dirt blown in from having the window open all the time. I have the willow colored interior and I'm afraid if I spray it with something or wipe it with anything wet that it'll leave a stain/watermark. Does anybody have any tips on how to clean a headliner?

 

mix woolite and water together in a spray bottle, spray your headliner with it, and wipe it off with a towel. it'll take you 5 minutes max to clean your headliner

 

Yes, it could be outside pollutants coming in the window. More commonly it comes from smokers who drive with a cracked window.

The woolite and water mentioned by big c will work fine. A general purpose cleaner properly diluted will work fine too. I recommend you have a clean preferably white towel that you spray the solution onto. Then rub carefully to clean the headliner. You do not want to soak the headline as it may lose it's shape and the glue used in it may fail.