The filament is made out of tungsten, why?

REASON FOR USING TUNGSTEN TO MAKE THE FILAMENT:

The filament is a small thin wire between two big wires which is generally found in light bulbs.  The electric current passes through filament and produce the light.

Hence the filament material need to handle high temperature. It also has to handle expansion and contraction while the heating and cooling. So the material need to be more flexible. In this case tungsten has a high melting point and can handle the heat and also the expansion and reduction well.  Hence, Tungsten is used for making the Filament.