Injection and blow molding leads in most cases to preferrential orientations in semi-crystalline polymer parts connected with an anisotropic thermal expansion behavior. In order to quantify them a model based on a lamellar elementary volume (EV) was developed allowing for calculating the 3 ultimate coefficients of thermal expansion (CTE) in space depending only on stiffness (moduli of amorphous phase and crystalline lattice moduli along and perpendicular to the polymer Backbone) and the corresponding CTE properties attached to the EV and the crystallinity. The ultimative CTE can be used in combination with 2nd order orientation tensors according TUCKER's description of fiber orientation to calculate either thermal strains and CTE for given crystalline orientations or to extract the crystalline crientation in terms of tilt and Rotation angle from measurements of thermal strains. The model is applied to to parts a) blow molded with mold temperatures of 5°C & 50°C and stretch ratios of 2 and 3.4 before blowing, and b)injection molded with 2 PE grades and thicknesses of 2.5 mm & 4 mm. It was found that the blow molded parts exhibited higher preferrential orientations perpendicular to the extrusion direction whereas the injection molded parts exhibited higher orientation along the flow direction.