Which material is better for fan impeller for fire smoke extract fans and why?

The best solution is normally aluminum because of its light weight. SS can also be used but very expensive

as per many catalog the best material for impeller is made of stainless steel which provide more thrust and higher temperature resistance.

for medium  thrust we may use cast aluminium impellers or galvanized steel.

anyway we have to select the suitable material which met the application in the range of budget.

either aluminium or stainless steel can be used i would prefer stainless steel due to its high withstanding temperature capacity since the stainless steel is produce either by hardening,quenching method which is suitable to withstand higher temperature ranges