Amorphous single layered silica films deposited using industrially scalable roll-to-roll atmospheric pressure-plasma enhanced chemical vapor deposition were evaluated in terms of structure–performance relationships. Polarised attenuated total reflectance-Fourier transform infrared absorption spectroscopy and heavy water exposure to induce hydrogen–deuterium exchange revealed it was possible to control the film porosity simply by varying the precursor flux and plasma residence times. Denser silica network structures with fewer hydroxyl impurities, shorter Si–O bonds, decreased Si–O–Si bond angles and a greater magnitude of isolated pores were found in films deposited with decreased precursor flux and increased plasma residence times, and consequently exhibited significantly improved encapsulation performance.