There’s nothing worse than when you’re all set to kick off the next leg of your road trip, but your car windows and windscreen are foggy and obstructing your vision.

In these situations, you can become desperate to defog and continue your journey. In our complete guide, we’ll address the causes of your foggy car interior and the best cures and preventative measures.

With this information, you’ll be all set for your wintertime New Zealand adventure with GO Rentals. Check out our extensive range of vehicles to find the perfect car for your self-driving journey. 

Fog car windshield

How to defog car windows and windscreens: Key takeaways

In a rush to deal with a foggy car interior? Here are some rapid-fire tips:

  1. Many vehicles have demist functions for front and rear windscreens, which do a great job of dealing with condensation.
  2. To deal with foggy windows quickly, begin by first blowing cold air into your car cabin to dry out the air. Then, you can turn the air conditioner to a more comfortable temperature to finish the job.
  3. Humidity plays a big role in condensation collecting on your windows and windscreen. You can reduce humidity in your car with products like dehumidifier bags and by minimising the presence of wet items in your car.

Why do car windows and windscreens become foggy?

Before considering how to defog car windows and windscreens, it’s useful to understand why exactly these parts of cars become foggy in the first place.

Generally, fogged-up windshields and windows are the result of discrepancies in temperature. If the inside of your car is warmer than the outside temperature, condensation may be collected on the windows and windscreen inside your car.

Similarly, if the outside air is warmer than the temperature inside your car, fog might appear on the outside of your car.

Fog on the inside of windows and windscreens is also the result of humidity in your car. The more moisture that is present inside your car cabin, the greater the chance of serious fogging.

Certain situations can make foggy windows and windscreens more likely. For instance, if you park your car on a cold night and sit inside it for a long time, the interior side of your windows and windscreen are likely to fog up.

This is because your breath is warming up in the inside of your car as well as providing moisture that adheres to the windows and windscreens.

Foggy car interiors are also an unintended consequence of superior car manufacturing. Newer cars have superior seals compared to older models.

This means that it is increasingly difficult for moisture to escape vehicles. Therefore, there is more moisture in your car to collect on your windscreen and windows.

foggy car window

What is the best way to defog a car windscreen?

If your windscreen is foggy, the first step is to determine whether it is fogged on the inside or the outside. This can usually be achieved by simply turning on your windscreen wipers. If your windscreen is fogged on its exterior, you can often remove all the condensation with a few wipes.

Things can be more complicated when your windscreen is fogged on in the interior. The most conventional way is to simply use your car’s air conditioner.

Many cars have specific demist functions of their air conditioners which aim hot air at its front and rear windscreens at high fan speeds. These can typically get the job done quickly.

In some vehicles, demister settings initially blow cold air into the cabin. This helps to dry out the air in the cabin before transitioning to warmer air conditioning temperatures.

One tip to help along the process is to turn off air recirculation. Adding fresh air into your car cabin is a great way to help the defogging process. You can also achieve this by winding down your windows as you demist, helping to equalise the temperature inside and outside your car.

What is the best way to defog car windows?

When it comes to defogging car windows, there are some crucial similarities and differences with windscreens. Cars typically do not have demist functions that specifically target windows, nor do they come with window wipers. This can make defogging car windows more challenging.

If your windows are heavily fogged on their exterior, a cloth is a handy tool to wipe them down and get on your way. You can also use a cloth to speed up the defogging process on the interior of your car, although this is trickier and often less effective than using a cloth on the exterior of your car.

Use a microfibre cloth to help prevent streaking when trying this method.

Again, your air conditioner is your best friend when it comes to defogging car windows. While you don’t have targeted demisting functions available for car windows, it’s still the best way to address humidity and temperature in your car cabin.

Buttons on car dashboard

For faster results, you can begin by first blowing cold air into your car cabin, which helps to dry it out. Then, you can gradually turn it up to a more comfortable temperature. It’s also best to use the highest fan setting available.

Winding down your windows can also be a helpful method for defogging them. However, make sure you only wind them down a little bit so the majority of the window is still exposed to the controlled environment of the car cabin.

How can I prevent car windows and windscreens from fogging up?

If you simply can’t stand a foggy car interior, there are a few preventative steps you can take to stop your windows and windscreen from fogging up.

  1. Cleaning: The cleaner your windscreen and windows, the less surface area water vapour has to adhere to. Therefore, regularly cleaning your windscreen and windows is an excellent method for reducing fogginess in your vehicle.
  2. Dehumidifier bags: Dehumidifier bags are a popular product for reducing the amount of moisture in your car cabin. This means there is less moisture that will collect on your car windows and windshield. Follow manufacturer instructions and ensure these are replaced or dried as needed.
  3. Wet items: Another way you can stop moisture from collecting in your vehicle is to minimise the presence of wet items like umbrellas and wet shoes in your car. Remove these items from your car as quickly as possible. Storing them in your boot rather than your backseat may also help minimise their impact on moisture in the car cabin.

Tips for defogging car windows and windscreen

Here are a few general tips for defogging your car windows and windscreen:

  1. Patience: It’s best to exercise patience when dealing with a foggy car interior. Don’t be tempted to drive off without having proper visibility. Just wait and let your car’s air conditioner do its thing.
  2. Planning: If you’re travelling to New Zealand in winter, you will likely deal with a foggy car interior on at least 1 occasion. As a result, make plenty of time for your travel plans. You don’t want to be rushing to make an appointment only to have to deal with low visibility in your car.
  3. HVAC maintenance: A well-functioning HVAC system is essential for effective defogging. Ensure your air intake is clear of debris, and consult us or a mechanic if you are experiencing any issues.

Is it illegal to drive with foggy windows and a foggy windscreen?

There are laws and regulations in New Zealand that mean driving with a foggy car interior could land you in hot water.

Section 8.8 of the Land Transport (Road User) Rule states the following:

  • “A driver of a motor vehicle fitted with a forward windscreen must at all times keep the windscreen clean and clear so that the driver’s view forward is not impeded or obstructed.”

The Land Transport Act 1998 also contains language that could make driving with a foggy car interior legally risky. Section 8 of the Act states:

  • “A person may not drive a vehicle, or cause a vehicle to be driven, carelessly or without reasonable consideration for other persons.”

Keep this in mind the next time you’re in a rush and consider not properly defogging your windscreen.

Explore New Zealand with GO Rentals

Foggy windows are most common in New Zealand in winter. Now, you have the knowledge to take on your Kiwi adventure no matter the temperature.

We have the accessories you need for a successful winter journey, including snow chains and ski racks. You can also enjoy a range of perks including unlimited kilometres on your trip and free basic insurance included on all hires, with upgrades available. With 24-hour AA roadside assistance included as standard, you are never too far away from help in a GO Rentals car. 

We’ve had the pleasure of sending many of our customers to explore the wintertime attractions of New Zealand. Here’s what Lindsay, an entrant in our Snap Happy photo competition, had to say about their GO Rentals adventure:

“A window of great weather allowed us to use our GO rental to access the Southern Alps. We spent a week split-boarding, ski touring and climbing in an amazing setting.”

GO Rentals snap happy review

Hire a vehicle from one of our 9 locations today and get GOing on your unforgettable adventure.