The PBF-LB/M process is highly suitable for the additive manufacturing of complex parts with precise geometrical accuracy using metallic powders. However, certain unknown variables exist within the process. Particularly, the thermal conductivity introduces a significant level of uncertainty due to the substantial impact of heat transfer from the part solid to the bulk material. Insufficient experimental data on the thermophysical properties of powder and a limited understanding of the influencing factors further exacerbate this issue. This study presents the thermophysical properties of steel powders commonly employed in the PBF-LB/M process, utilizing a newly-developed powder container for laser flash analysis. Through a quantitative comparative analysis with the corresponding solid materials, it has been demonstrated that the chemical composition and microstructure play a secondary role in determining the heat conductivity of the powder bed. Instead, it is the powder size distribution that serves as the primary parameter governing the observed behavior. Display omitted •Thermophysical properties of powder were measured by dynamic measurement method.•A novel measurement device for powder measurements using laser-flash was used.•Powder properties differ significantly from corresponding solid properties.•Particle size is the main influence on the thermophysical properties.