There are tons of ways to defog windows in the winter. Any from self proclaimed experts. However, there are multiple different theories, so which one to choose. Well, all you need is hot air on full blast, A/C on,so it will pull moisture out of the air and from your windows. Turn off inside air circulation (the car with a circle on it.) It brings in cold air which can't hold much moisture, so it will help. Lastly, crack your windows a bit, as many as you can. Even for a few seconds, it exchanges the humid air with the outside cold air. So, all in all, Heat on full blast, A/C on, inside circulation off, and crack the windows.
Source
