Michelin Pilot Sport tyre. The two main synthetic rubbers in car tyres are polybutadiene rubber (BR) and styrene butadiene rubber (SBR). They are typically used in combination with around 20% natural rubber (NR). Tyres used in more demanding applications, such as trucks and aircraft, contain a higher proportion of natural rubber. A whole host of other materials and additives are used, including steel cable, reinforcing textile and fillers (predominately carbon black and silica for conductivity and enhanced resistance to tearing and abrasion) to give the desired performance. Image Michelin.