Despite the advances in our understanding of the microscopic structure of hair, a complete molecular representation of the hair surface that incorporates the key chemical details is lacking. Given the complex molecular structure of the hair surface, that includes amorphous heavily crosslinked proteins and varying amounts of 18-MEA attachments based on the location of the fiber, atomic resolution structures are not fully accessible. Representative models have been proposed using molecular modeling techniques, each with their own advantages and limitations. For instance, one of the earliest models of the hair surface contained Langmuir monolayers of 18-MEA. Upon comparing the packing density, surface tilt angle, and order parameters of this model against eicosanoic acid, the authors highlighted the differences in monolayer ordering due to the methyl group at the 18th position in 18-MEA. A subsequent study created a model keratin fiber surface using an ultra-high sulfur protein (UHSP) with 18-MEA attached via a thioester linkage to surface accessible cysteine residues. By incorporating a model beta sheet protein substrate, the authors were able to reproduce the approximate thickness of the outer surface of human hair and wool layer as measured by X-ray photoelectron spectroscopy (XPS) and density of the exocuticle . A separate study used a reduced model of the epicuticle surface with 18-MEA bound to graphene sheets . By reducing the complexity of the surface system, Cheong et al. were able to calculate the free energy of the fatty acid layer as a function of separation distance in an attempt to optimize the packing density. This simplified model suggested an optimal range of 18-MEA separation distances between 4.92 and 6.51 Å. Their conclusion agreed with previous experimental characterization of wool surfaces , but not the frequently cited value of 9.36 Å . The reduced model, as the authors claimed, agrees with transmission electron microscopy (TEM) measurements but not XPS characterization.