Polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) films were treated with an atmospheric-pressure plasma (APP) jet and a 172-nm ultraviolet (UV) excimer light in air. The advancing and receding water contact angles on both films decreased after the treatments, especially after APP treatment. After the treatments, the hydrophobic recovery was observed and almost diminished within a week. The dispersive component of the surface free energy of the two polyester films did not change due to the APP and UV exposure, whereas the acid-base component drastically increased after the treatments. The X-ray photoelectron spectroscopy results showed that the polyester film surfaces were oxidized by the treatments. From the AFM images, the topographical change on the film surfaces due to the treatments was clearly observed. It was found that the APP treatment of the PET film prevented the deposition of particulate soils in air due to the decrease in the contact area between the film and the soil particle. Furthermore, the soil release in the aqueous solutions was promoted as a result of the hydrophilization of the polyester films due to the APP treatment. IntroductionPolyethylene terephthalate (PET) has high strength, high resilience, good impact resistance, and outstanding processability. Because of its many applications, PET is one of the most common plastics available today. One of the most common applications is for drink bottles, including those for soft drinks. PET films are used for balloons, flexible food packaging, space blankets, and as a carrier for magnetic tape, or a backing for pressure-sensitive adhesive tape. PET is used for major textile fibers, which are known as polyester.Polyethylene naphthalate (PEN) is a new-generation polyester polymer of naphthalene-2, 6-dicarboxylate, and ethylene glycol. Although PEN is more expensive than PET, PEN exhibits higher dimensional stability, shrinkage resistance, and temperature stability, and better barrier properties than PET. Owing to its superior modulus of stiffness, PEN can be used to produce films of equivalent strength to PET but at a lower thickness and narrower width. Such films are advantageous for electrical applications,