In Hall-Heroults process the main reagent is mixed with

${\mathrm{Na}}_3{\mathrm{AIF}}_6\to \mathrm{Cryolite}$
Al₂O₃ is mixed with cryolite
Cryolite improves the electrical conductivity of the cell as Al₂O₃ is a poor conductor. In addition, the cryolite serves as an added impurity and lowers the melting point of the mixture to about 950° C .