If you wear glasses be very cautious about heading out into a very, very heavy fog. Your face shield will mist over solidly and you cannot just lift the shield because your glasses will now do the same thing. All the shield 'wax' will not help much - because the drops are not big enough to gather & roll off, just a total misting over will happen - which is no problem for those who don't wear glasses. They just lift the shield a motor on, slowly.
This becomes a real adventure at night!
Stay put until the fog diminishes.
Stig