The best ways to avoid foggy windows

Know your enemy

The fog on your windows materializes when humidity in the air turns into millions of teeny tiny water droplets on our windshield. No one is surprised by this, but thinking a bit about how and why it happens may still be worthwhile.

In below zero temperatures, every part of your car gets cold, including the air locked in it. As we’ll get back to, cold air is dry. Trapped moisture freezes and hides in fabrics and on surfaces.

When you get in, you bring heat and humidity. The more of you there are in the car, the more you provide. There’s snow on your shoes and your clothes, your breath is steamy, and your skin may be sweaty. Perhaps you’ve even brought some freshly brewed coffee into the equation. Since you feel cold, you also turn on the heating system.

It’s physics

Warm air is warm because it has more energy. That energy makes water molecules in the air move faster and further apart. That energy also causes evaporation of moisture in your car, filling the air with more vapor.

The process reverses where the warm and watery air inside your car crashes into your still cold windows. The air loses energy until the water molecules move slowly and tightly enough to condense back into water droplets. The droplets stick to the glass, and now you can’t see where you’re going.

How to avoid foggy windows!

To fight the fog, you must limit moisture, ensure that everything has the same temperature, or preferably both. Here are some ways to do that.

Preheat your car

Aside from parking inside, the most reliable way to prevent fogging is to preheat your car with an interior heater. Preheating ensures that everything, including the windshield, has a high enough temperature from the get-go. If you suspect that the air is especially humid, you can open the doors and windows for a few seconds to let it out.

Read more about interior heaters or our full WarmUp preheating system.

Try to be dry

Brushing off your clothes and getting in sideways to kick the snow off your boots are familiar rituals to most. So is putting wet things in a bag. While helpful, some water always gets in. Besides, your breath has a 100% relative humidity, and your body holds 37 degrees Celcius. When it’s freezing outside, much of the problem is you.

Soak it up

One way to limit moisture on your windows is to make sure it ends up somewhere else. Various dehumidifier products are available for purchase, but a sock filled with fresh cat litter might work just as well. Just remember to replace filling after a while.

Use the AC

Yes, even in winter. Your air conditioning works by removing humidity and heat from the air and moving it outside, which is just what you need. Using it carefully lets you maintain a comfortable temperature.

Keep it clean

Fog needs something to cling to, so the cleaner your windshield is, the less foggy it will be. Particles from your car interior and the road outside creates a film on the inside of your windshield. Remember to clean it off from time to time. And never use your hands to wipe away the fog. That only makes matters worse.

Stay cold

Literally. Leaving the heating off and opening the windows to let out warmth and moisture is an effective way to avoid foggy windows. However, most think this cure is worse than the disease.

Read more about why you should preheat your car

Read about the 4 best reasons to install a battery charger in your car