In the last 10 years, efforts have been devoted to increase the inherently low thermal conductivity of the currently available silica bricks used in coke oven linings, in order to optimize the coking process, Pursuing the same objective in this work, we comparatively evaluated the effect of collateral additions of silicon carbide on the thermal diffusivity of a typical silica refractory base composition, as well as the production of silicon carbide in situ by direct reaction of silicon metal and carbon black. The experimental technique employed was the diffusivity flash technique. It was found that controlled amounts of silicon carbide can increase by almost 100% the thermal diffusivity of the base composition. It was also observed that a direct relationship exists between the phase transitions of cristobalite and the dependence of thermal diffusivity on temperature. In addition, a hysteresis behavior observed in the measured thermal diffusivities was minimized upon repeated heating and cooling cycles.