The atomic structure of carbon fiber is similar to that of graphite, consisting of carbon atom layers arranged in a hexagonal pattern. Depending on precursors and manufacturing process, the layers might be turbostratic, graphitic or in a hybrid structure. In graphitic structure the sheets are stacked parallel in a regular fashion. Bonding between planes is weak, giving graphite its soft characteristics. Carbon fibers made of PAN are turbostratic and can provide higher strength, while pitch can provide higher modulus.