Not taking BOPP A into account, the roughness data may suggest that a smoother surface results in better barrier properties after AlOx coating. In the case of BOPP D and PET, we however assume that the barrier improvement is caused by the change in surface chemistry whilst for BOPP B and C there are further differences that are known to have an impact on barrier properties. Antiblock particles protruding up to several microns fromthe film surface will quite likely result in defects in the coating