The paper presents results of tests concerning influence of accuracy in measurements of selected thermal properties of materials of a ceramic mould, insulating mat and an alloy itself on effects of simulation of a casting process provided for elements of an aero-engine. A simulation process was realized by means of the PROCAST program. In initial simulations, thermal parameters were applied and they are accessible in literature and concern materials of a mould and nickel superalloys. Results of simulation revealed presence of numerous defects in a form of gaps, pores and cracks. These results were proved in trial casting. In consequence, it was impossible to select correctly right casting parameters. In order to solve this problem, a value of thermal conductivity was defined experimentally and basing on it, coefficients of heat exchange in metal – mould, mould – insulation mat systems were defined as well. A value of partial coefficients of heat exchange was used to determine values of substitute coefficient of heat exchange for the whole metal – mould, mould – insulation mat systems. By introducing the got data, one managed to define parameters of a casting process, providing improvement in a level of quality of cast elements.