Tundish flux or powder provides multiple functions. Firstly it insulates the molten steel both thermally (preventing excessive heat loss) and chemically (preventing air entrainment & reoxidation). The quality of the flux being used also play vital role, such as nitrogen pick-up was reported to be reduced from 16ppm to 5ppm, from ladle to mould by changing tundish flux with lower SiO2 content, in one of South American steel works. Secondly, in ideal circumstances, the flux also absorbs inclusions to provide additional steel refining.

A common tundish flux is burnt rice husk, which is inexpensive, a good insulator, and provides good covering without crusting. However, rice husk is high in silica (>80%), which can be reduced to form a source of inclusions. They are also very dusty with their high carbon content around 10%, may contaminate ultra low carbon steel. Basic fluxes (CaO-Al₂O₃-SiO₂ based) are better than rice husk to avoid any Si or C inclusions in tudishes. Basic fluxes have been reported to reduce the total  oxygen content of steel bath, also. 

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