This paper shows a study on the variation of the flow ratio between oxygen and Hexamethyldisiloxane (HMDSO) in a hollow cathode arc PECVD process. Dynamic deposition rates were measured between 300 and 500 nm ∗ m/min. The deposited plasma polymer films were analyzed using visible light spectroscopy, X-ray photo-electron spectroscopy (XPS), X-ray reflectivity (XRR), Fourier-transformed infrared spectroscopy (FTIR), Scanning electron microscopy (SEM) and water vapor transmission rate (WVTR) measurements. The deposited samples were compared to a reactively sputtered SiO2 thin film. By increasing the oxygen to HMDSO flow ratio, the chemical, density and optical properties of the coating approached the sputtered SiO2 film. However the permeation barrier of the SiO2 film only shows a slight improvement over that of the bare PET substrate. The organic coating with high power and low oxygen flow, which was deposited with a deposition rate of 450 nm ∗ m/min, approached the barrier of the sputtered SiO2 thin film with a WVTR of 0.16 g/(m² day)