This article presents a comprehensive review of the modern thermo-conductive materials that have potential to improve the heat extraction in electrical machines by conduction. Currently, there is a significant interest in thermal design and analysis of electrical machines as the demand for high power/torque density is substantially raised in applications such as marine, aerospace, e-mobility and rail. Thermal design engineering has become very important to develop smaller and more efficient electric motors, therefore electrical machine designers need to be more informed with the recent development in novel thermo-conductive (insulation) materials. Such developments can provide enhanced thermal characteristics for high power dense electrical machines. It is reported that high voltage electrical insulations can have more sophisticated thermal properties with the recent advancements in materials science. This study aims to inform electrical machine designers with and without a thermal background about recent thermo-conductive materials. Thus, a profound understanding can be gained in thermally conductive materials for the use of numerous applications in electrical machines for which thermal management is a crucial aspect of the overall multi-physics design and optimization process.