While 18-MEA has been identified as the primary lipid of the hair surface, other free lipids have been shown to exist on the surface. XPS measurements of the carbon/nitrogen ratio on hair surfaces have been used to estimate the lipids on the hair surface as a function of washing and treatment . Based on these data, it was suggested that free lipids are bound to the F-layer noncovalently and 18-MEA ``straighten out to accommodate the free lipid to approach the expected length of 18-MEA" . In the absence of free lipids, it is expected that 18-MEA will fold back on itself at the surface, as demonstrated by the tilt angles of the hair models in this paper. To explore this, we adsorbed two common fatty acids: stearic and palmitic acid on the model surface. These fatty acids were chosen as they are known to exist in hair fibers and also used as ingredients in hair conditioning products . In order to elucidate this problem, computational simulations were then performed in both the presence and absence of water. In vacuum, stearic and palmitic acid intercalate with the 18-MEA on the surface and are able to cover the KAP5-1 surface, regardless of the surface density for the three models (Supplementary Figure ).