The properties of the cell wall are determined by its structure and by the properties of the wood polymers. In this study, the influence of the elastic constants of the three wood polymers on the elastic modulus of the cell wall was investigated. Cellulose was found to dominate the properties in the longitudinal direction. In the transverse direction, the effect of the properties of hemicellulose was more pronounced. The results show that it is possible to reduce the discrepancy between experimental and modeled values of the transverse modulus to a large extent by lowering the assumed values of the elastic constants of hemicellulose and lignin. The thickness and fibril angles of the S-1- and S-3-layers were also found to be important parameters for the transverse properties of the fiber wall. These two layers should not be neglected when transverse elastic properties are related to cell wall structure.