FLiBe is a molten salt that is a mixture of lithium fluoride (LiF) and beryllium fluoride (BeF2).
Because it’s a liquid, it can act as both a Fusion breeding blanket and a coolant for heat transfer inside a Nuclear fusion reactor.
FLiBe has a high boiling point, so it can absorb a lot of heat while remaining at atmospheric pressure.
Its low electrical conductivity will allow it to move easily despite the reactor’s strong magnetic fields.