Why Can't You See Clearly Through the Rear Windshield on Rainy Days?

[DiPaislee]

On rainy days, the rear windshield of a car becomes unclear due to the temperature difference between the inside and outside of the vehicle, causing the glass to fog up. Defogging Mode: Cars come equipped with a defogging mode. When you encounter this situation where the windshield is unclear on rainy days, you can turn on the air conditioning and select the defogging mode. Wipers: Proper use of the wipers can prevent rainwater from staying on the glass for too long. Cleaner with Dry Cloth Wipe: Mix cleaner with water, apply it evenly on the glass with a sponge, and wipe it dry with a towel after it dries, leaving no watermarks. Generally, this can effectively prevent fogging for up to 20 hours.

[LeTheo]

It's hard to see through the rear windshield on rainy days, and after driving for over a decade, I know how common this issue is. Raindrops on the glass scatter light, creating a blurry view. If the wipers are old or not working efficiently, water droplets accumulate faster. The rear window defroster is crucial—it heats the glass to evaporate droplets, and if it fails, it’s a real problem. High humidity inside the car during rain also causes fogging on the inner side of the glass, making matters worse. I make a habit of keeping wiper blades clean, replacing them regularly, and checking the heating circuit. I also use the AC to ventilate and reduce humidity. If visibility drops, I slow down or pull over temporarily, avoiding reversing to prevent accidents—safety first. Preventive maintenance is always the best approach.

[Nascimento]

Recently encountered foggy rear windows while driving in the rain, which was quite scary. It might be due to rainwater clumping on the glass, making reflections unclear, or the defroster not working, preventing water droplets from dispersing. I’ve experienced sudden temperature changes inside the car causing worse fogging on the inner side, and had to use the AC’s cold air to dry it. If the wipers are broken, rainwater can’t be cleared—my friend’s car was like this and nearly caused an accident. Now I’ve learned to clean the glass surface and use the defogger to stay alert. When visibility is poor in the rain, I slow down and rely more on the mirrors, avoiding risky lane changes, especially since beginners tend to panic. Checking small vehicle issues can prevent bigger problems.

[VanBeckett]

The rear windshield's poor visibility is often caused by dense water droplets formed due to rainwater surface tension, with failed heating wires unable to remove water beads, worsening the blur. Wiper malfunctions with insufficient sweeping force leave residual water flow, while damaged glass coatings and stains cause slow water droplet attachment. Internal fogging occurs due to high humidity, requiring ventilation activation to dry it promptly and maintain clear visibility. Maintaining the heating system and regular cleaning are key countermeasures.