When Disc Brakes became popular Asbestos was used as the material for Brake Pads. This was because asbestos offered a resilient yet a very heat resistant material at a low cost.
However, towards the turn of the last century, environmental concerns forced auto companies to scout for alternatives to Asbestos.
Various fibres like Rubber, Carbon, Kevlar and Glass were held together with resins to form an “Organic” alternative to Asbestos. This helped to make the first Environment Friendly (read Asbestos Free) Brake Pads.
Further developments allowed the use of metals like steel, iron, copper, etc. to be incorporated in the formulations. The metal helped in better dissipation of heat away from the rotor and more efficient brake cooling. This was the advent of the “Semi Metallic” variety.
The latest technology in brake pads uses “Ceramic” formulations consisting of Copper Fibres embedded in ceramic material. This allows them to handle extremely high temperatures, and give quieter braking without compromising on performance. Therefore, Ceramic Pads are the best all round option for surest braking. However, they may not be material of choice for extremely cold temperatures.