This article is aimed at investigating the effect of a calcined kaolin filler (CKao) on polyethylene terephthalate (PET). The influence of a silane coupling agent, chain extension, and post extrusion uniaxial hot-stretching on the final properties of the produced composites were studied as well. PET-CKao films were prepared via melt blending using a twin-screw extruder followed by stretching above the glass transition temperature at controlled conditions. The morphology of the composites before and after stretching was observed by SEM. Rheological measurements were also performed to characterize the polymer melts. Mechanical and optical properties as well as the oxygen transmission rate of the composites were also investigated. The results showed that addition of CKao particles, even at low filler content, improved drastically the mechanical and barrier properties compared to the neat PET. This effect was more pronounced in case of hot-stretched samples. The main drawback observed with these CKao particle composites was an increased haze. Processing parameters including stretching temperature and stretching ratio were found to have a significant effect on the final properties; however, the influence of the stretching rate was negligible. (C) 2014 Society of Plastics Engineers