What Causes Fog Inside the Glass?

[DeJason]

The reasons for fog inside the glass and their solutions are as follows: 1. Closed balance holes: The absence or improper placement of air pressure balance holes and drainage holes prevents water from draining, leading to long-term evaporation and moisture entering the glass interlayer, causing fog. Solution: Use insulated glass whenever possible, as it can significantly reduce this phenomenon. 2. Improper positioning: Incorrect installation position of the spacer bar, where it is adhered along the edges of the glass without leaving a gap, makes it prone to direct contact with rainwater. After absorbing moisture, it generates vapor between the glass panes. Solution: Install glass spacers, ensuring the spacer bar is placed 1-2mm away from the glass edges and 3-4mm from the bottom edge of the glass. This prevents direct contact with water. Additionally, choose high-quality spacer bars with low water absorption. 3. Inadequate sealing: Poor sealing of the glass, with uneven or incomplete application of sealant around the edges. Solution: Ensure tight sealing of the glass, paying careful attention during the application process.

[LaBrianna]

Driving for long periods often leads to foggy windows, which is ultimately caused by temperature differences—cold glass surfaces paired with warm, humid air inside the car. Factors like human breath releasing moisture, wet clothes left in the car, or water tracked in from rainy shoes all contribute to increased humidity. The worst scenario occurs in winter when warm air from the heater hits the icy glass, instantly condensing into droplets. Even blasting the AC too hard in summer can cause this. I remember a long drive last year during heavy rain when the windshield fogged up so badly I couldn’t see the road, forcing me to roll down the windows and endure freezing cold air. Later, I discovered that wiping the inside of the glass with soapy water and letting it dry could help for a few days. For a permanent solution, though, using the AC’s defogging mode to blow dry, cool air onto the glass is the way to go.

[Darin]

I've noticed that fogging tends to occur more frequently on days with high humidity. Even the slightest moisture inside the car can quickly obscure the windows. From a physics perspective, when the glass temperature falls below the dew point of the air, water vapor condenses into fog droplets. In winter, interior window fogging is common because warm, humid cabin air meets cold glass surfaces. Conversely, summer often brings exterior window fogging - for instance, when AC vents blast cold air onto the windshield, causing hot, humid outside air to condense. During one family road trip, spilled drinks from the backseat children caused cabin humidity to skyrocket, instantly frosting up the windshield. Now I've developed the habit of activating external air circulation immediately after starting the car to balance interior and exterior humidity levels. For emergency defogging, directing cold AC airflow straight at the windows works fastest, but remember to engage the AC's dehumidification function.

[ValeriaMarie]

This happens every day when driving for ride-hailing. The principle of fogging is simple—it's caused by temperature and humidity differences between the inside and outside of the car. Common scenarios: passengers getting in and out on rainy days bringing in moisture; multiple passengers breathing in winter producing water vapor; residual humidity inside the car after parking meeting the cold glass in the early morning the next day. I have an emergency method: immediately reduce humidity (open windows or use air conditioning dehumidification) and increase glass temperature (blow warm air directly) simultaneously. I found that poor-quality window tinting makes fogging more likely. When passengers leave fingerprints or grease on the glass, the fogging the next day becomes more severe. Now I've developed a habit of wiping all car windows with alcohol wipes every day after finishing work.