What effect does spraying rain repellent on a dry windshield have?

Spraying rain repellent on a dry windshield can lead to smearing and streaking, which ultimately reduces visibility. When applied to a dry surface, the repellent does not have a proper medium to adhere to or spread evenly. As a result, the product may not bond correctly with the glass, leading to uneven distribution that can distort vision. This uneven surface can create reflections and distortions that impair the driver's ability to see clearly, particularly in varying light conditions.

In contrast, a windshield should ideally be cleaned and slightly wet when applying such products to ensure even coverage and optimal function. The correct application of rain repellent on a clean, wet surface enhances its effectiveness by enabling it to form a proper bond, leading to improved visibility by ensuring that rainwater beads off the surface rather than smearing.