Abstract This work is carried out within a university project, which is focused on the life cycle efficiency of products. This project is conducted because of the growing interest towards environmental protection, which requires a sustainable development of the industrial progress.A Dutch-EVO concept car was taken as a vehicle for the research within this project. One of the innovations in the Dutch-EVO project is the use of modern lightweight materials to reach the sustainability of the concept car.A polymeric composites reinforced with natural fibers have been chosen as one the most challenging materials to be applied in automotive structures. Structural and semi-structural application of these materials is considered as vital for car sustainability. Their low density, good strength and low price make them very attractive for automotive sector.The current field of natural fiber composites application is limited to non-structural automotive components because of the low impact properties, poor moisture resistance and high variation in their mechanical properties. The variation in their properties appears due to large heterogeneity of the reinforcement. A new engineering approach is required to account the heterogeneity at the design stage.The polymer matrix composites reinforced with non-woven natural fiber mats are researched. A novel technique is proposed for the estimation of heterogeneity in their properties. The technique is based on the analysis of the digital image of the reinforcement using the signal processing technique. The derived parameters of heterogeneity then are used to generate the in-plane heterogeneity of the material. Then, the developed heterogeneity generation procedure generates the complex material heterogeneity by the addition of several low-order heterogeneities generated simultaneously. The generated heterogeneity is correlated to the local in-plane variation of Young?s modulus of the composite material. This variation is realized in a FORTRAN procedure and implemented into MSC.MARC commercial finite element code.The resulting novel approach can be used for more reliable simulations than using traditional approach through more accurate description of local mechanical properties of the heterogeneous structures. Finally some future improvements of the developed approach are also suggested. General design guidelines using heterogeneous natural fiber composites are drawn in respect to design of automotive structures.@en