Question

which material is used in making plugs and switches​

Answer 1

The material is typically a polymer: either thermoset or thermoplastic. Most typically a thermoset. The properties of the material are specified by some code I am sure. When designing devices which carry voltage the spacing of the contacts is fixed so the material separating them has to have a low minimum insulating property. If I remember correctly this is called dielectric strength. Which is the voltage required to cause tracking along the material surface. Different countries have different voltages and different switch and plug configurations. The variation in these can be related to the material dielectric and voltage.

Answer 2

backlite a kind of strong insulated plastic is used