The carbon element is added to the common rubber material, which makes the rubber more tough and wear-resistant. Most running shoes use this kind of rubber, and the BRS letters are left on the back part of the sole of the running shoes to indicate that the carbon rubber is used in the outsole.

The structure of the sole is quite complex. In a broad sense, it can include all the materials that make up the bottom, such as outsole, midsole and heel. In a narrow sense, it only refers to the outsole. Generally, the common characteristics of the sole material should be wear-resistant, water-resistant, oil-resistant, heat-resistant, pressure-resistant, impact-resistant, elastic, easy to fit the foot type, not easy to change after shaping, thermal insulation, easy to absorb moisture, etc. At the same time, it should also cooperate with the midsole to have a braking effect when changing feet, not causing slipping and easy to stop. There are many kinds of materials for soles, which can be divided into natural and synthetic soles. Natural bottoms include natural bottoms, bamboo, wood, etc., while synthetic bottoms include rubber, plastic, rubber-plastic composite materials, recycled leather, elastic cardboard, etc.