A good carbon fiber frame has a mixture of different types of carbon fibers, each of which is used in different locations in the frame for very specific purposes. High-modulus fibers are expensive, so bicycle companies wisely use a relatively small amount of key areas like down extensions, bottom brackets and chainstays to resist the pedaling force and make the bike harder. But they are placed in the mold along with standard middle molds and high-strength fibers to create good carbon frame durability, performance and ride quality.
Carbon fiber sandwich foam is a great material for two reasons. First, the weight is lighter than almost any other material. Secondly, unlike metal, the stiffness of carbon fiber can be finely manipulated; its stiffness characteristics are only applicable to the unidirectional or long axis of the fiber itself, so the stiffness can be adjusted according to how the carbon fiber composite material is oriented or placed in the mold. This is what is called Anisotropy. In contrast, metals are isotropic, exhibiting the same strength and stiffness properties along any axis of the material.