What Causes Car Windows to Freeze?
3 Answers
Car windows freeze due to high humidity inside the vehicle and a significant temperature difference between the interior and exterior. Here are solutions to prevent car windows from freezing: Parking in a basement or indoors: When temperatures are low, it is recommended to park the vehicle in a basement or indoors, minimizing outdoor parking. This effectively reduces snow and rain accumulation on the windows, thereby decreasing the frequency of freezing. Using the heating system to defrost: Start the vehicle and turn on the heating system to defrost the windows using warm air. However, the main drawback of this method is that it takes time and consumes fuel. Avoid locking the car immediately after parking: When parking, do not lock the car and leave immediately. Instead, open the windows briefly to balance the indoor and outdoor temperatures, which helps reduce freezing.
I was really puzzled by this during my last business trip. The car was parked outdoors overnight, and the windshield was covered in ice crystals in the morning. The main reason is that residual moisture inside the car condenses when it gets cold. When you park the car, the residual warmth from the air conditioning and the moisture from breathing adhere to the glass. When the temperature drops below freezing in the early morning, the moisture instantly freezes into a layer of ice. This is more noticeable when the air humidity is high, and the same principle applies to the windshield fogging up when you breathe on it in winter. Another detail many people overlook is that rainwater carries road dust onto the glass, forming a thin film when it dries, which crystallizes directly when the temperature drops at night. The solution is simple: open the windows for ventilation for 1 minute before parking to remove moisture, or make your own antifreeze spray by mixing half a bottle of alcohol with water and spraying it on the glass.
Research has been conducted on this physical phenomenon: the core reason for car glass icing is the phase change caused by temperature differences. During daytime driving, the glass temperature remains above the dew point, keeping water vapor in a gaseous state. After parking at night, the glass cools rapidly to below -3°C due to the faster heat dissipation of the metal frame, causing moisture in the air to condense on the warmer glass surface. For example, in cold regions with outdoor parking, ice formation is highly likely when ambient humidity exceeds 70%. Another critical factor is the glass material—windshields are more prone to icing than side windows due to the poor heat retention of their laminated structure. Prevention methods are scientifically grounded: using a car cover with 70% shading can block heat exchange, or applying a specialized hydrophobic coating on the glass surface alters its thermal conductivity coefficient.
