3 ways to stop your car windshield frosting overnight

Frost forms when a surface cools below freezing and below the dew point, which happens most easily on clear, calm nights. Glass loses heat to the open sky quickly, so windshields are among the first parts of a car to frost over. Here are three ways to stop it, and a few things to avoid.

1. Cover the glass

This is the most reliable option because it stops moisture from landing on the glass in the first place.

• Use a windshield frost cover (sold in many sizes and styles), or an old blanket, towel or a flattened cardboard box cut to size.
• Make sure the cover is held in place, either with flaps shut in the doors or with magnets or straps, so wind doesn't take it.
• Cover the side mirrors with a bag or sock if they're prone to ice.
• Check your owner's manual before you lift the wiper arms off the glass. Doing so can stop the blades from freezing to the windshield, but some vehicles have specific instructions.

Tip: shake off any snow before you lift the cover, so it doesn't slide down onto the car or onto you.

2. Park smart

• Garage or carport: a roof reduces how much heat the glass loses to the sky. This is the biggest win if you have one.
• Under cover: if you can't use a garage, parking beside a building or under an overhang helps more than an open lot.
• Face the windshield east if you can. The sun hits it first in the morning and starts to melt the frost before you're out the door.
• Avoid parking under trees that drip. Sap, sticky leaves and bird droppings are a hassle to clean off.

3. Cut the moisture inside the car

If frost forms on the inside of the glass, the cause is humid air in your cabin freezing on the cold surface. Reduce the moisture:

• Knock snow off your boots before getting in, and shake out wet floor mats. Consider rubber mats that you can empty out.
• A few minutes before you park, run the defrost with the A/C on (it dries the air) and set the fresh-air setting instead of recirculating.
• Don't leave wet gloves, hats or umbrellas in the car overnight.
• If your cabin stays damp, a moisture-absorbing product (such as a silica-based car dehumidifier) can help. Follow its label.

What not to do

• Don't pour hot water on frozen glass. The sudden change in temperature can crack the windshield.
• Don't use your wipers to scrape ice. You can tear the blades or burn out the wiper motor. Use a scraper and the car's defroster.
• Don't leave the car idling unattended while you wait inside. It wastes fuel, can be a theft risk, and some municipalities restrict idling. Check local rules.

A simple morning routine

• Remove the cover (shake the snow off first)
• Start the car and turn on the defrost and A/C
• Clear snow from the roof, hood, lights and all windows
• Use a plastic scraper on any leftover ice
• Make sure you can see out of every window before you drive