Electrical conductivity is simply the measure of how easily electrons—the carriers of electric charge—can move through a material when a voltage is applied. The question of why copper wire conducts electricity far better than carbon fiber is fundamentally a question of atomic structure and chemical bonding. Copper excels because its electron arrangement creates an efficient path for charge flow, while the structure of carbon fiber inherently restricts electron movement. The vast difference in performance comes down to the material science of metals versus covalently bonded nonmetals.
The Atomic Structure of High Conductivity (Copper)
Copper is a metal, and its superior electrical performance is a direct result of its metallic bonding structure. Each copper atom has one electron in its outermost valence shell, which is weakly held and easily shed into the material’s bulk structure. When copper atoms form a wire, these valence electrons become delocalized, meaning they are no longer associated with a single atom. Instead, they form a collective “electron sea” that flows freely around the lattice of positively charged copper ions. This highly mobile cloud of charge carriers is the defining feature of a metal.
Copper’s atoms arrange themselves in a highly ordered pattern called a face-centered cubic (FCC) crystal structure. This regular, repeating lattice allows the free-flowing electron sea to move with minimal scattering or resistance. The combination of readily available charge carriers and an unhindered path for movement makes pure copper one of the most efficient electrical conductors available.
How Carbon Fiber’s Structure Limits Electron Flow
Carbon fiber is a nonmetal composed almost entirely of carbon atoms, which form strong, directional bonds. The core of carbon fiber’s structure is \(sp^2\) hybridization, where each carbon atom forms three robust covalent bonds with its neighbors. These three bonds rigidly lock three out of the four available valence electrons into fixed positions, severely limiting the number of electrons available to carry a current.
The atoms arrange themselves into flat, hexagonal sheets, similar to the structure found in graphite, but these sheets are highly disordered and stacked irregularly in a turbostratic arrangement. Although the fourth electron (the pi-bond electron) is delocalized and allows for some conductivity along the length of the sheets, the overall movement of charge is constrained.
This sheet-like structure causes the material’s conductivity to be highly anisotropic, meaning it conducts electricity much better along the fiber’s axis than across it. Electrons can hop relatively easily along a single sheet but struggle to jump the tiny, disordered gaps between the stacked layers. Furthermore, when carbon fibers are used to create a composite material, they are typically bound together by an insulating polymer resin, which acts as a barrier that dramatically impedes the flow of current between fibers.
Quantifying the Performance Gap
The performance difference is quantified by comparing electrical resistivity, which is the measure of a material’s opposition to the flow of electric current. Lower resistivity means better conductivity.
Pure copper exhibits an extremely low resistivity of approximately \(1.7 \times 10^{-8}\) ohm-meters (\(\Omega \cdot m\)) at room temperature. Carbon fiber materials have longitudinal resistivities that are orders of magnitude higher, typically ranging from \(1.5 \times 10^{-5}\) to \(1.5 \times 10^{-4} \ \Omega \cdot m\). This quantitative comparison reveals that copper is roughly 1,000 to 10,000 times more conductive than a raw carbon fiber filament. When the fiber is embedded in an insulating polymer to create a composite, the overall conductivity can drop even further, making a typical carbon fiber composite nearly 100,000 times less conductive than a copper wire.