Carbon black contains more than 99% pure carbon. Other components are oxygen, hydrogen, and nitrogen. It is available in powder or beads (pellet) form. The black particles are 10nm to approximately 100nm in size and fuse into chain-like aggregates, which define the structure of individual Carbon Black grades. Depending on the production process parameters, Carbon Black types differ in particle size, structure, surface chemistry, porosity, and many other characteristics. The properties of most Carbon Black grades are determined by industry-wide standards. The American Society for Testing and Materials (ASTM) is the most widely used, especially for Rubber Carbon Black grades.

Surface area measurement gives an indirect characterization of carbon black particle size. Typical carbon black particle sizes for furnace blacks range from approximately 8 nanometers to 100 nanometers. Smaller particle size increases the specific surface area (m2/g) of the carbon black. Smaller particle size and higher specific surface area lead to increased reinforcement, increased abrasion resistance, improved tensile strength but higher hysteresis. To disperse smaller particle size, carbon black requires increased mixing time and energy. Particle size and its distribution can only be measured using a transmission electron microscope. Based on surface area, furnace blacks fall within N100 to N700 series. (N) denotes normal curing material.

Carbon black particles collide with other particles and become an aggregate. Groups of aggregates are loosely held together in agglomerates. The number of primary particles and degree of branching in the carbon black aggregate determines its structure level, which has a direct impact on several important in-rubber properties. For example, increasing carbon black structure increases modulus, hardness, electrical conductivity, and improves dispersion of the carbon black, but also increases compound viscosity. Measures of aggregate structure may be obtained from its shape distributions from oil absorption (OAN) or void volume analysis.

This fundamental property of carbon black can affect the measurement of surface area resulting in a total surface area (nitrogen specific surface area or NSA) larger than the external or non-porous surface area (statistical thickness surface area or STSA). Increasing the porosity reduces the elope density of the aggregates. This results in a higher volume fraction of carbon black at a given loading that leads to an increase in compound modulus and electrical conductivity.

The organophilic nature of the carbon black surface lends itself to a very synergistic and high level of carbon black-elastomer interaction that greatly improves the abrasion resistance, tensile strength, hysteresis, and modulus of a rubber compound, without coupling agents or intensive mixing. The surface characteristics of carbon black are difficult to precisely define, but the surface structure of carbon black is believed to be composed of graphene layers oriented in a tile-like fashion with exposed edge sites that contain various functional groups composed of hydrogen and oxygen. In furnace blacks, due to shorter reaction times, result in numerous sites for chemical bonding with elastomers.