Semi-Metallic: This friction formulation contains 30 to 65 percent metal, which can be a combination of steel wire and iron powder. This formulation has fast heat transfer and the higher metal content, the better the performance.
Low-Metallic or Low Metallic NAO (Non Asbestos Organic): This formulation usually contains about 15 to 20 percent metal in combination with other compounds. This product performs best when the original equipment material is NAO as well. This formulation does not transfer heat as fast as the Semi-Metallic formulations.
NAO (Organic): This formulation is generally referred to as organic. This formulation contains non-asbestos fibers with various compounds and on occasion, some metal. This formulation may be quieter, but may not have a high heat rate transfer.
Ceramic: Ceramic disc pads contain ceramic fibers and other ceramic compounds and may have some non-ferrous metal. Some attributes associated with ceramic pads include a quieter and smoother operation and may have less vibration than other friction formulations.
As this list indicates, the variety of friction formulations available in the aftermarket provides the end-user and installer with greater choices of friction materials. The brake pad aftermarket is a growth market and the various formulations available indicate that aftermarket manufacturers are innovating to provide the end-user with great options.