Question

why does the outer part of the bulb gets hot the filament is hot? is not the outer part of the bulb an insulator? ​

Answer 1

In an electric bulb current is passed through a filament due to heating effect of current filament glow up and gives out light.

But all these happens due to heat and there are three ways of transformation of heat conduction, convection and radiation.

By the property of transformation of heat i.e radiation heat transforms from filament to glass as a combined effect glass also heat up although it is an insulater.

hope it helps...