After all the fires this past summer in NorCal, I decided to check the cabin air filters in our cars. All I can say is O-M-G that's NASTY! You can get a cheap $10 filter like the FD920 Cabin Air Filter for Ford Focus, or upgrade to a nice HEPA based one like the PureFlow HEPA Cabin Air Filter PC6174HX
Whatever you do - just do it! Look at our old filter compared to the new one! Seriously disgusting!
If you don't know how, it's a really simple process on the Focus family. You just need one torx bit and everything else is pretty much hand driven.
