In the development of next generation high strength steels, the current and future problems have been focused on availability of new mold fluxes for continuous casters. Due to the reactions and heat transfer issues associated with these new steel grades, calcium-silicate based fluxes are not able to function in the capacity to optimize the thermo-physical properties represented by the acronym “APRIL (Absorption, Protection, Radiation, Insulation, Lubrication)”. Thus, radical approaches to developing mold flux powders are required, but without measured data of the thermo-physical properties such as viscosity, crystallization, thermal conductivity and others the development efforts can be considerably hindered. FactSageŽ and related thermodynamic simulations can provide the flux engineer the much needed qualitative and semi-quantitative trends with regards to the effect of temperature and composition on these thermo-physical properties. This study looks at the applicability of FactSageŽ to mold flux developments and future needs for improvement to expand its use.