well it could be because of the heat. if its cold out and you have the heat on in the car, then you will get hot and that will cause the window to fog.
moisture from your breathing for example condensing on the cold glass
It is called condensation, warm and humid inside, cooler outside.
Windows fog because the glass is cold and the humidity is high inside the car. It has nothing to do with the age of the car. Try turning the fan up to circulate the air better, and if that doesn't work, turn the AC on -- but turn the heat up so it doesn't get cold. That will do it for sure.
Two people, breathing heavily. There's a lot of water vapor in your breath, and when two people are going at it they breathe a lot more causing more water. If it's cold outside, the windows fog up like crazy.
Rub them with soap then clear the soap of with a cloth or paper this will reduce the amount it wil fog in the future as well.
Fog forms on bathroom mirrors and car windows when the water vapor in the air condenses on the glass. This is due to the temperature difference between the glass and the air.
No the blend door not functioning will not cause fog; it may however prevent the windows from being defogged or defrosted. If the widows only fog up when the defroster is on, then you either have a coolant leak in the heater core or your air conditioner compressor isn't working (the AC is used to dry the air when the heat is on).
It will fog up with moisture, the inside windows in the car, also accompanied with the sweet odor of coolant.
heater core is going bad.
When the windows begin to fog, the physical change is: condensation of water vapor.
Well there is an easy way and a hard way, first, you could only do whatever it is you are up to in the winter, it will be colder and when you blow on the windows mist or fog comes up, or you could boil a kettle in their. Hope you got a backseat and a boyfriend or a girlfriend ; )
Not using bright lights, turning off music/radio so you can hear traffic at intersections, opening windows at intersections, getting fog lights on the car, and using only low beans on the car.