Technical Abstract: The Young's modulus is a measure of the inherent stiffness of an elastic material. In the case of cellulose, it quantifies the ability of the material to undergo changes in length as tension or compression forces are applied. The modulus can be calculated by performing tensile tests on cotton fibers or, as in this study, by stretching molecular models in a computer program. However, considerable disparities between values from different experimental tensile tests and among molecular modeling calculations are observed. With this study we attempt to ascertain the roles of intermolecular hydrogen bonding and other intra- and intermolecular details from molecular models in modulus determinations. To achieve this, modulus calculations with empirical force fields and quantum mechanics were performed with cellobiose models capable of intramolecular hydrogen bonds as well as some analog models that cannot make hydrogen bonds.