Aims of this work were research of the material transfer properties influence on heat transfer and subsequent search of the heat dissipation optimization ways. Subject of the research was plastic heat sinks for retrofit LED lamps. To achieve this aims numerical simulations of free convection flow were performed which were coupled with simulation inside solid parts of the heat sink. In this study, parametrical researches took place. During this study, heat transport properties of the heat sink material were varied. Derived results allowed to make conclusion about optimal heat transport properties of the plastics which can be used in retrofit LED lamp production. In addition, some heat sink structure improvements were proposed.