Carbon Fiber Reinforced Polymers (CFRP) are a promising engineering material because of their multifunctionality and desirable mechanical, electrical, and thermal properties. The mechanical and fracture properties of CFRPs rely on effective stress transfer from the bulk matrix to individual carbon fibers. Pristine carbon fibers (CF) are chemically unreactive and smooth, which inhibits stress transfer mechanisms and makes CF susceptible to matrix debonding. Current composite research aims to improve the synergy between the CF and surrounding matrix by engineering the interphase. The composite interphase is characterized by mechanical properties deviating from the fiber and matrix properties. Carbon nanotubes (CNT), graphene nanoplatelets, and other carbon nanofillers have been studied extensively for their interphase-enhancing capabilities.