Recently, plasma-polymerization at atmospheric pressure has become a promising technology due to its reduced equipment costs and its possibility of in-line processing. This paper focuses on plasma deposition by an atmospheric pressure dielectric barrier discharge (DBD) using hexamethyldisiloxane (HMDSO) as gaseous precursor. HMDSO plasma-polymerized films are deposited onto polyethylene terephthalate (PET) films using argon and different argon/air mixtures as carrier gases. The chemical and physical properties of the obtained coatings are discussed using contact angle measurements, Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM). Contact angle and FTIR results show that the composition of the gas phase and the chemical structure of the obtained coatings are clearly correlated. When pure argon is used as working gas, the film is polymeric with a structure close to [(CH 3 ) 2 -Si-O] n . However, with increasing air content, a gradual change is observed from organic polydimethylsiloxane-like coatings to inorganic, quartzlike deposits. AFM results clearly indicate that with increasing air content, the deposition rate decreases, while the surface of the deposited films becomes rougher. From this point of view, the capability of controlling both chemical and physical properties of the plasma-polymerized films by varying operation conditions opens interesting perspectives.