Brake Dust on On Cars and trucks
The unsightly brake dust that we all see on automotive wheels is 92% Fe which simply put is in part iron caused by abrasion of the cast iron brake rotor by the pad and secondly fibers from the semi metallic elements of the brake pad. The remainder of the dust residue is carbon content within the brake pad.
99% of automotive brake pads made these days are made as a semi metallic meaning a bundle of steel fibers compressed and fused together with other additives. The steel fiber content can be up to 30% of the pad and this abrasive material is what scratches your brake rotor and causes the dust.
Non metallic pads such as those made with Twaron or kevlar fiber are only available as an upgrade in the aftermarket and very few manufacturers opt to use these more expensive materials simply for build cost purposes. These pads are known an organics and often outperform and outlast their semi metallic counterparts as well as reducing rotor abrasion and dust caused in the braking action.
Brake dust on Motorcycles
is almost 100% from the contents of the pad itself and the much harder wearing heat treated stainless steels on motorcycles only wear down very slowly unlike cast iron in automotive brake systems.
All you have to do to avoid dust on a motorcycle is use a pad that contains minimal steel fiber.
Some sintered metal pads may appear to be copper in color and material yet many include steel fiber or powder or more expensive stainless steel powder.