Which allotrope of Carbon do we use in Carbon Fiber?

Carbon fibers are composed of carbon atoms linked in a longitudinal direction. The carbon atoms are bonded together in microscopic crystals that are more or less aligned parallel to the long axis of the fiber. This crystal alignment gives the fiber its high strength-to-volume ratio. These carbon atoms are bonded in the form of an allotrope known as graphite. In graphite, each carbon atom is connected to three other carbon atoms in a plane composed of hexagonal structures. These planes can slide over each other easily, making graphite a good lubricant and giving it its distinctive sheen. However, when these layers are aligned and bound together in a certain way, they form a strong, lightweight fiber known as carbon fiber.

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