Why does my PPF have dirty lines or yellow edges?

Dirt lines along film edges form when grime, wax and water collect in the tiny gap where the film meets the paint, especially with pressure washing or drying aids that leave residue. Yellowing is usually UV ageing of the film or its adhesive, more common on older or lower-quality films. Clean edges gently with a soft brush and a suitable cleaner; do not pick at them. Yellowed film cannot be cleaned back to clear and needs replacing.