The description is somewhat vague. Is the OP describing the insulator for the brass contactor ring that is turned by the light switch spider or is it something else? If it is this part then it is made of Micarta such as used for circuit boards.
There are four different types of light switch as well so a person has to be specific or post a photo. This link has a photo of all four types.
https://www.mafca.com/downloads/Semi...ex%20Janke.pdf