What heat- and friction-resistant material was once used extensively in vehicle brakes and clutch linings?

Asbestos is the correct answer because it possesses unique properties that made it highly suitable for use in heat- and friction-resistant applications, particularly in vehicle brakes and clutch linings. It has excellent thermal resistance and can withstand high temperatures without losing structural integrity. Its fibrous nature also provides good friction characteristics, which enhance the performance and safety of braking systems.

Due to these desirable qualities, asbestos was widely used in these components for many years before serious health risks associated with asbestos exposure became widely recognized, leading to stricter regulations and a decline in its use. While other materials, such as fiberglass, rubber, and ceramics, have their own applications in automotive components, they do not match the heat and friction-resistant capabilities that asbestos originally provided. Fiberglass, for example, is more commonly associated with structural applications and insulation, rubber is used for its elasticity, and ceramics are typically utilized in components that require wear resistance rather than heat conductivity within braking systems.