Why does the car windshield feel oily on rainy days?

[McLena]

Car wax and dust can easily get trapped in these tiny pores, forming a contamination layer—the oily film layer, which is also the main reason why the front windshield often doesn't stay clean. Below is some relevant information: Windshield: Car windshields are generally made as a single large curved piece, with a certain curvature on all sides. This curved glass is a highly technical product, both in terms of the manufacturing process and the fitting during assembly, as it involves numerous factors such as vehicle model, strength, heat insulation, and installation. Function of the Windshield: Tempered glass refers to ordinary glass that has been quenched to create internal stresses, thereby strengthening the glass. When impacted and shattered, the glass breaks into small pieces with blunt edges, reducing the risk of injury to passengers.