This article reports the results of the extensional viscosity ( E) of polyolefins composites films. The test material was composed of ternary MDPE/iPP/CaCO3 composites with a calcium carbonate content of 48-72% by mass. The concentrations of the composites and reference materials that were PE-MD/iPP mixtures are summarized in Table 1. For all materials the viscosity curves (rotational rheometer) and the change in mass flow rate were determined. Two types of investigated films were produced: cast films and blow films. The extensional viscosity of films (thickness approximate to 80 m) was performed on a SER-2 Universal Testing Platform. The influence of the addition of calcium carbonate, extrusion techniques and the direction of sample cut (MD and TD) to change the extensional viscosity were discussed. The extensional viscosity measurements ( E) were taken at a temperature of 140 degrees C and for a strain rate (Hencky strain rate) of center dot H=0.1, 0.2 and 0.5 s(-1). POLYM. ENG. SCI., 59:E155-E163, 2019. (c) 2018 Society of Plastics Engineers