This work demonstrates epitaxial relationships between the crystal structure and growth faces of nylon 66 on high-modulus graphite fibres and explains observations in the literature. It also extends the concepts and applies them to the more complicated system of isotactic polypropylene (i-PP) on highly graphitic carbon fibre structures. The proposed arrangements are based upon matching a polymer’s crystalline structure, along its growth face, to possible graphitic structure dimensions along carbon fibre surfaces. The matches involving substrates and overgrowths in both cases are nearly perfect, being within 5%, thus accommodating favourable low-energy positioning of the polymer’s crystal structure. The relationship involving nylon 66 allows this polymer’s chains to orient along fibre surfaces between graphite basal plane edges. This epitaxial relationship is consistent with the literature and is used to predict the orientation of crystalline i-PP chains when deposited on carbon fibres. To preserve a low-energy epitaxial relationship, the i-PP chains are suggested to be oriented some 78 degrees across stepped graphite basal plane end surfaces and are most likely oriented at 78 degrees to the fibre direction. Additional discussion, arising from complexities in the case of i-PP, concerns the relation between the number of possible polymer nucleation orientations and the nucleating ability of a given fibre surface.