The thermal properties of the mould steel influence the cooling situation in the injection moulding process. There are some experimental studies investigating the influence of special mould materials like copper alloys, but these studies are limited to a few polymers. In the present work, an extensive parameter study with the commercial injection moulding simulation software Autodesk Moldflow Insight was performed to further analyse the influence of the mould steel on the injection moulding process, specifically the cycle time and warpage behaviour. The investigated part was a square box with two thickness variations (1 mm and 3 mm) to see also the influence of the part thickness. A conventional mould steel (W300 from Böhler, Austria) was compared with a newly developed steel grader (W620), featuring approximately double the thermal conductivity compared to the conventional grade. In a systematic parameter study more than 150 simulations were performed with 18 different polymers covering the most common material families including amorphous, semi-crystalline, unfilled as well as glass fibre reinforced polymer grades. The whole mould including the cooling system was modelled with a 3D-mesh and a transient cooling simulation was used. As expected, the higher thermal conductivity reduced the cycle time – surprising was the range of this effect, though (< 5 % up to 25 % of cycle time reduction), which strongly depends on the used polymers and the related processing conditions, but also the part thickness. For the extent of the cycle time reduction a correlation was found with the ratio of the difference between melt and mould temperature to the difference between ejection and mould temperature. With this correlation it was possible to predict the range of cycle time reduction for other polymers based on those three temperatures. Furthermore, the simulations showed that the higher thermal conductivity of the mould steel resulted in a reduced warpage of the part.