Tree sap is a complex organic resin that acts as a powerful adhesive. When deposited on a vehicle's surface, it begins to harden through evaporation. As the sap cures, it creates a localized "hot spot" that attracts solar heat, leading to thermal expansion differences between the sap and the paint.

This often results in "etching", a permanent physical indentation in the clear coat. Because sap is non-polar, standard soap and water will not dissolve it; it requires a specialized solvent or a high-lubricity surfactant to break the bond without scratching the substrate.