What Are Brake Pads Made Of? Friction Material Composition Explained

A brake pad is not a block of one material. Its friction surface is a carefully balanced composite in which the binder, fibres, abrasives, lubricants, fillers and friction modifiers must work together across temperature, pressure, speed and humidity. Changing one ingredient can improve one property while weakening another.

The short answer

Modern disc-brake friction material is normally a resin-bonded composite. Typical formulations combine a binder that holds the matrix together, reinforcing fibres, abrasives that help generate friction and clean the rotor surface, lubricants that moderate wear and friction, fillers that control physical properties and cost, and other friction modifiers used to tune response.

The exact recipe is application-specific and often proprietary. Ingredient names alone cannot tell a buyer how a pad will behave on a particular vehicle. System design, processing, geometry and validation are equally important.

The six functional ingredient groups

This list describes functions, not a universal recipe. One ingredient may serve more than one function. Graphite, for example, can act as a lubricant and influence the formation of the friction layer. Particle size, shape and dispersion may matter as much as the ingredient name.

Ceramic, NAO and semi-metallic are broad families

Aftermarket labels simplify a much more complex formulation space:

• NAO or non-asbestos organic materials generally use an organic resin matrix with fibres, fillers and friction modifiers, without asbestos.
• Ceramic is usually an aftermarket term for a low-metal or non-steel formulation that uses ceramic or mineral components and is tuned for comfort, dust appearance and stable everyday response. It does not mean the pad is made from fired ceramic like a tile.
• Low-metallic formulations contain a limited amount of metal to improve heat transfer or friction response while retaining many NAO characteristics.
• Semi-metallic formulations contain a more substantial metallic fraction and are often selected where thermal conductivity, load capacity or firm response is important.

What happens at the friction surface

Braking is governed by the interaction between the pad, the disc and a dynamically changing contact layer. Small contact plateaus form, wear and reform. Material can transfer between the pad and rotor, while heat and wear debris alter the interface. The result depends on speed, pressure, temperature, humidity and the previous braking history.

This is why a single room-temperature friction number is not enough. SAE J866 provides a uniform way to classify friction coefficients measured under its test method, but the standard itself warns that the code does not establish overall performance requirements and cannot reliably predict complete brake-system behaviour.

Why two similar ingredient lists can perform differently

Performance is affected by the entire production route: weighing accuracy, mixing uniformity, preforming, pressure and temperature during moulding, curing, grinding, scorching where specified, slot and chamfer geometry, and the attachment to the backing plate. Density, porosity, hardness and compressibility must remain controlled from batch to batch.

Noise illustrates the interaction. Research has linked squeal propensity not only to friction level but also to contact conditions, pad hardness, damping, porosity, wear and chamfer shape. A supplier therefore needs more than a formula; it needs a controlled process and a validation plan.

Environmental and market requirements also shape the recipe

Friction formulations change as environmental rules evolve. The U.S. Copper-Free Brake Initiative, for example, set a nationwide pathway to reduce copper and certain other constituents in motor-vehicle brake pads. Similar-looking pads made for different markets may therefore use different ingredient systems.

Do not infer compliance from colour, price or a generic material label. Ask for the marking, test method and documentation relevant to the destination market and vehicle category.

What a professional buyer should verify

1. Application definition: vehicle, axle, brake system, load and duty cycle.
2. Formulation identity: a controlled compound code, not only “ceramic” or “semi-metallic.”
3. Performance evidence: appropriate dynamometer, wear, noise and environmental data for the application.
4. Mechanical construction: backing plate, attachment method, shim, chamfers, slots and hardware.
5. Process control: batch traceability and checks for thickness, compressibility, hardness and bond integrity.
6. Market documentation: the approval, registration or environmental marking actually required in the destination market.

Technical references

• SAE technical paper: fibres and functional ingredients in copper-free friction composites
• SAE J866: friction coefficient identification and environmental marking
• U.S. EPA: Copper-Free Brake Initiative
• SAE technical paper: porosity, hardness, compressibility, wear and squeal