Definition
The ability of a material or system to resist changes under ultraviolet exposure. It is not the same as a measurement of how much UV reaches the substrate.
Why it matters
A claim of resistance to yellowing does not establish complete UV filtering. Use a specific transmission or performance document if that property matters, and avoid extending a statement for one film to all products.
Apply the concept
PPF lifespan, inspection and removal
Distinguish service life from warranty and plan what to do when film ages, lifts or is damaged.