RTV Silicone rubber composites have many applications to form many medical products for example orthotic insoles. Improved its mechanical properties using talc results on the reduce the pain due to planar stress on human foot joints. In the previous study, improved hardness of insoles from RTV silicone rubber with talc reduces the planar stress and the foot position, thereby reducing fatigue when walking. However, mixing silicone rubber with talc will cause porosity. This study aims to reduce the porosity and minimize the trapped air by adding 30% talc into silicone rubber using vacuum die casting. In the experiment, the pressure variation was determined at -0.4 bar, -0.6 bar, -0.8 bar, and -1 bar through a mold size of 45 mm in diameter and thickness of 7 mm. Fluidity, density, porosity, and hardness were tested during the experiment. The results show that decreasing the vacuum pressure increases the density and hardness due to the size and distribution of porosity being smaller and more homogeny. Furthermore, it also produces higher fluidity. However, the specimens produced by vacuum casting are not partially filled. This is due to the large shear stress on the walls of the mold and increasing viscosity due curing process.