Abstract: A process for treating dyed and/or undyed polyester materials with an ultraviolet absorber to overcome or inhibit the destructive effects of ultraviolet light is disclosed. The polyester materials may be in the form of a film, yarn, textile products which are woven or non-woven. The process includes the steps of contacting or immersing the polyester material in either an undyed or dyed condition in a bath containing a non-volatile liquid polyhydric alcohol and an agent which is soluble in the polyhydric alcohol and compatible with the polyester material in effective concentrations such that effective amounts of the agent are incorporated into the polyester material together with the polyhydric alcohol to ensure substantially complete penetration of the agent in the polyester material and then removing excess bath solution by washing.