This study considered the effect of shielding gas parameters (composition, supply method and flow rate) on the post-weld thermal properties (thermal expansion, specific heat capacity, thermal diffusivity and thermal conductivity) of the weld metal in gas metal arc welding. This is of importance as the thermal properties influence the temperature distribution and therefore the residual stresses and distortion present within the final structure. Due to the lack of accurate thermal data, computational modelling techniques (such as FEA and CFD) used for modelling the welding process generally make assumptions regarding the material thermal properties, and it is often the case that the parent material thermal properties are extended to the weld metal, introducing errors to the simulation. It was determined that the weld metal posses considerably different thermal properties to the DH36 grade steel parent material and that the shielding gas parameters significantly alter key thermal properties of the solidified weld metal. A lower shielding gas flow rate exhibited beneficial properties including a lower thermal expansion and higher specific heat capacity and thermal conductivity than a higher shielding gas flow rate.