Carbon fibre is the number one choice for performance bikes right now. Nearly all of the mainstream manufacturers make their cheaper performance bikes from aluminium but their high-end models from carbon fibre. Manufacturers can use carbon fire to produce frames that are very lightweight, yet stiff in certain areas to maximise power transfer and more flexible in other areas for comfort. Carbon fibre can also be shaped relatively easily for aerodynamic efficiency.
Carbon fibre is made up of a very hard but brittle material, the resin, and an incredibly strong but flexible material, the carbon fibres. Together, they support one another.
The resin locks the fibres in place, giving the composite rigidity, while the fibres prevent the propagation of cracks in the resin, giving the material strength. When carbon breaks it does so with a tear, crush or puncture; it doesn’t develop small cracks which could fail later like a steel or alloy frame might.
Unsurprisingly, the cheaper you go with carbon the lower the quality. While a top-end race frame from a big name brand will be built to a high standard the same can’t be said for bikes produced at the opposite end of the market.