Carbon fiber is not a single category

Carbon fibers come in various forms: raw filaments or sheet fibers (continuous fibers) and short fiber fibers, which can be used as sheets or chopped very short fiber clumps. The chopped fibers are used in products like pedal bodies. The sheet style is the most common in bicycle frames, what it sounds like: a continuous sheet of carbon fiber (called a layer), bolts that look like fabric, usually quite wide, wrapped around a giant spool.

Carbon fiber is not the only one in use

We say "carbon fiber", but what we really mean is "carbon fiber composite material" This is not the only material in your frame. This is because carbon fiber has incredibly rigid properties. The disadvantage is that it is quite fragile by itself and is easy to split and break. In order to maintain its ability, it is suspended in a gel-like material called epoxy resin before molding to form a composite material.   

resin accomplishes two tasks. First, it holds the carbon together, the individual fibers within the two plies, and once cured, the orientation of the two layers to each other is sufficient. Second, the resin adds critical toughness and durability. It is a slight plastic that deforms under impact to help absorb crashes or sharp blows without causing critical splits between fibers.

Application of carbon fiber

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 downswing, bottom brackets and chainstays to resist the pedaling force, making 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.

Material advantages of carbon fiber

Carbon fiber is a great material for two reasons. First of all, we know that the weight is lighter than almost any other material. Second, 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 the so-called anisotropy. In contrast, metals are isotropic and exhibit the same strength and stiffness properties along any axis of the material.   

Engineers use complex software programs, taking into account the carbon grade, resin, shape, size and direction of the carbon fiber layer, even in the mold. This is how the framework is optimized for extreme mildness or rigidity, or both, but these programs and graduate degree expertise to run them are expensive.