Injection moulding of polymers is a well-established technique for the production of increasingly complex articles, and residual molecular orientation is a matter of considerable interest. A single matrix of commercial atactic polystyrene was systematically blended with deuterated polystyrene chains of five different weight fractions and the orientation investigated using small angle neutron scattering (SANS), optical birefringence and thermal shrinkage. The strengths and limitations of the experimental techniques used to measure residual orientation are explored and highlighted the unique contribution of SANS to observe ensemble averaged molecular orientation using deuterated polymers. The residual molecular orientation was found to vary with the molecular weight of the deuterated chains with an increase with increasing molecular weight. The observed correlations lead to a better understanding of the processing parameters that influence the degree of residual orientation on the molecular scale. Such information is valuable in the selection of the polymer matrix, mould design, and processing conditions. POLYM. ENG. SCI., 58:1332-1341, 2018. (c) 2017 Society of Plastics Engineers