ok..
condensation...
the qty of moisture that air can hold changes with temperature. in short, warmer air can hold more moisture than cold air, - this is why you get the term 'relative humidity' as this takes into account air temperature. eg 50% relative humidity at 20 degrees - if the air then reduces in temperature the relative humidity % will increase even though the qty of moisture in a volume of air is the same.
when the air gets to 100% it cannot hold the qty of moisture and so condenses..
this time of year is perfect for condensation as air is relatively humid and then reduces in temperature.
example:
you get in the car, you breath, your clothes are damp, you keep the windows closed as its cold - these all increase the humidy of the air.
in tandem you turn the heaters on, this allows the air to hold more moisture...
then the car is parked up.
the air reduces in temperature, the car is relatively sealed so the air doesn't circulate/change and eventually the air reaches the point it cannot hold the moisture, (dew point)
the glass of the car, particularly the windscreen tend to be cold (compared to say the dash) and so the air across glass tends to be the area in which condensation occurs.
(similar to people getting condensation in headlights, particularly after washing the car, and it may go if you put the lights on and hear up the air)
anyway, what can we do to reduce this:
using air con is mentioned above, this can dehumidify the air and reduce the chances of condensation.
but other factors can be:
1 - the wet rag you used to wipe the window, - this sits in the car? adding to humidity? (consider a sealed bag)
2 - the wet coat, did you leave this in the car? - in fact anything wet, damp or moist in the car? (the mrs?)
3 - probably not in this case, but older leon's suffer with leaking door seals...
4 - when near to your destination the cabin will be warm and humid. so try and reduce the humidity before you park up. open the windows and give the cabin a blow through. (you can also turn the heaters off but not critical).
5. Are you (or your passengers) chubby, sweaty people?
6 are you indulging in in-car aerobics which could be producing sweat, you dirty, dirtyboy?
these will
help reduce the opportunity for condensation, - but ultimately its something that occurs and you cant get rid of it entirely. - air circulation is the typical approach, (eg extractor fans or open window in bathrooms). so an option is also to leave the window slightly open, but then this can allow rain in!