Originally Posted by CollectiveInk

One of the other culprits can be the headliner. Every car I've owned that had a vinyl headliner (read almost all hondas) fogged worse than those with a fabric headliner, as vinyl won't absorb the extra humidity like fabric will (but it won't sag a readily as fabric will )

I've never had good luck with Rain-x. Not saying it doesn't work, just not for me, especially here in TN where 80+ percent humidity is normal.

The one thing I KNOW works is shaving cream. Yup, good ol' fashion $.79 / can white shaving cream (not the gel stuff). You can test it out in your bathroom even. Coat/wipe half of your mirror with the shaving cream (you don't need a lot) and leave the other half not done. (It wipes off pretty easily, just a few extra paper towels or cloths) and then let the hot water run in the shower with the door closed. You'll see.

WARNING! - We all know shaving cream can cause discoloration so use with caution. You might have to put a towel on the dash or wherever to guard against drops.

Just another question... is it all your windows that fog or just certain ones/areas?