The classical lamination theory is widely used for the calculation of the mechanical properties of reinforced plastics and stress distribution inside laminates. The resulting Young’s moduli along the fiber direction are close to the achievable properties of unidirectional reinforced laminates [1]. However in most applications woven fabrics are used that lower the stiffness of the composites [2]. The influence of undulation and waviness of the fibers on the mechanical properties is yet to be explicitly specified. This article deals with the description of fiber undulation as well as the coherence between the geometry of fabrics and the achievable laminate properties. In order to get improved estimations for the Young’s modulus, a new, easily applicable method is introduced to consider the undulation of fibers in the calculation process of the classical lamination theory (CLT). The results show that the given method leads to diminishing the error of the ordinary process.