The spark plug insulator is usually made of what type of material?

The spark plug insulator is typically made of ceramic material because of its excellent electrical insulating properties and resistance to high temperatures. Ceramics can withstand the extreme heat generated in an engine environment, which ensures that the spark plug functions efficiently and reliably over time. The insulating qualities prevent electrical leakage and maintain the necessary voltage required to create a spark for ignition. Additionally, ceramics are durable and can withstand the mechanical stresses encountered in an engine's operating conditions.

Other materials, like metal, would conduct electricity rather than insulate it, while plastic may not have the temperature resistance needed for a spark plug's operation. Glass is also not suitable due to its brittleness and inadequate performance under high-temperature conditions typically found in engines.