Extrusion blow molding is a successful processing method to produce hollow plastic parts for the packaging and automotive industry for more than 30 years. Unfortunately, it exist no adequate simulation software for the prediction of final part properties in blow molding in contrast to injection molding. The final properties of blow molded parts depend on the processing parameter such as melt temperature, extrusion speed and wall thickness. Especially shrinkage and warpage are important phenomena which affect the geometry and as a result the performance of the final part. Therefore, these phenomena have to be considered in part design and process development. The amount of shrinkage and warpage depend on the coefficient of thermal expansion (CTE). The classical method is a linear description of the CTE which is only valid in a certain temperature range and only for homogeneous materials. In reality, CTE depends strongly on local crystallinity and molecule orientation. Currently there is no non-linear description of CTE based on the anisotropic morphology of semi crystalline polymers. This study will propose a new non-linear CTE model for semi crystalline polymers based on crystallinity measurements and theoretical values of the direction depended young’s modulus and CTE from literature for high density polyethylene HDPE. HDPE specimens were made with different mold temperatures and draw ratios to determine the influence on the anisotropic morphology of the parts. The thermal properties of HDPE were measured by differential scanning calorimetry (DSC) and thermomechanical analysis (TMA) in respect to the extrusion direction. These results were used to correlate and validate the new non-linear CTE model based on the measured crystallinity with the results of the thermal expansion. The new non-linear CTE model shows a good correlation with the results of the thermal expansion and gives the option to improve existing simulation software for blow molding in further studi