Kevlar and Carbon Fiber are two modern composite materials that are renowned for being both strong and light. They're frequently used in extreme situations that demand high performance and strength, such as aviation, high-end sports cars and high impact body armour. Though they are often used together, the two materials differ in some important areas.
Carbon Fiber is technically a cloth, woven from many thin strands of graphite. The strands are laid over a mould and pasted into place using a tough epoxy resin.The crossed positioning of the strands is vital to ensure maximum strength and responsible for the "checkered" pattern seen on many Carbon Fiber components. Kevlar, on the other hand, is constructed on a microscopic level, chaining together man made molecules into a rigid polymer crystal. The resulting solution can be spun into strands or poured like a liquid.
Both Carbon Fiber and Kevlar are extremely strong, but in slightly different ways. Kevlar is extremely rigid, until the point at which it starts to buckle under compression. As its structure is compromised it will buckle quickly. Carbon Fiber is generally less resistant to piercing forces due to its stranded construction, but it is largely unaffected by high temperatures, something that can weaken Kevlar.
Carbon Fiber components are extremely light, as their stranded construction means they can be produced at very low thicknesses provided they are not required to be particularly strong. As a result, Carbon Fiber is usually the material of choice for builders of light aircraft and race car bodies. Where extra strength is required, a layer of Kevlar will often be pasted into the Carbon Fiber shell to reinforce it. This is common in the construction of safety gear, such as motorcycle helmets.
Kevlar is generally not flexible. Since its structure can be severely compromised by altering its shape, Kevlar items are usually produced to be stiff and rigid. This is certainly the case with body armour plates, which are intended to stop a weapon or projectile, while transferring as little of the energy to the body as possible. Flexible plates would allow a concentration of force at the point of impact, which would be transferred to the wearer's body. Carbon Fiber can be made to be quite flexible, depending on the thickness of the sheet used. Its flexibility is one of the ways in which it dissipates impact energy, making it more suitable for breakaway items, such as car body panels.