E12 light bulb bases are made of phenolic resin. This plastic material is known for its resistance to heat, strength, and non-conductive characteristics. In the early days of lamp sockets, a material called Bakelite was used to manufacture e12 bulb socket. In fact, Bakelite was the name of those lamp holders.
![PGZ 315 lamp holder PGZ18 light socket adapater](https://lightbulbsocket.com/wp-content/uploads/2019/05/PGZ-315-Ceramic-Lampholder-2-300x300.jpg)