What are the reasons why PPF turn yellow?

The first-generation PPF, due to technological limitations, had topcoat layers with insufficient density to resist the intrusion of tiny external substances into the TPU base material. Therefore, the first-generation PPF required regular maintenance known as "film care." This maintenance involved applying hydrophobic automotive wax to the surface of the film. The wax served to seal the capillaries on the topcoat layer, preventing external substances from penetrating through and reaching the TPU base material.

If there was heavy rainfall or the car was washed several times, this wax could wear off, losing its protective function. As a result, the PPF could become dirty. If left untreated and external foreign materials penetrated the lower layers of the film, the film would lose its luster and turn yellow.