## 4 Conclusions  
According to the conducted research and the analysis of the achieved results, the following conclusions and remarks can be drawn. Bending strength: The highest bending strength was observed for plywood containing lupine flour and coconut flour as fillers. These materials appear to contribute positively to the mechanical performance of the plywood, making them suitable candidates for applications requiring high structural integrity. Water absorption (as pure flour): Bamboo flour and lupine flour exhibited the highest water absorption among the tested fillers. This characteristic may influence their behavior in adhesive mixtures and the final plywood product, especially under conditions of high humidity or exposure to moisture. Shear strength: During the shear strength tests, plywood containing coconut flour, bamboo flour, and lupine flour demonstrated the best results. This indicates that these fillers can enhance the bonding properties of the adhesive mixture, contributing to the overall durability of the plywood. Spirulina: Despite its promising properties, spirulina exhibited the lowest water absorption values. While this might suggest good moisture resistance, it likely contributed to the lower strength results than other fillers. This finding highlights the importance of balancing water absorption and adhesive compatibility when selecting alternative fillers. The influence of filler composition on the mechanical properties of plywood can be attributed to the physical and chemical characteristics of the fillers, their interaction with the adhesive matrix, and their ability to modify the bonding environment. Coconut and lupine flours improved plywood mechanical properties due to their balanced water absorption capacity and structural compatibility, facilitating efficient adhesive penetration and forming robust bonds. Coconut flour, in particular, exhibited high MOE and MOR values at optimized filler concentrations, suggesting a significant contribution to stiffness and strength. Conversely, spirulina, with its low water absorption and brittle glue structure, resulted in lower strength parameters, highlighting the importance of moisture compatibility. Bamboo and lupine flours exhibited high water absorption, potentially altering adhesive consistency and application ease and impacting mechanical strength. High water absorption influenced density profiles, leading to adhesive penetration and bond quality variations. Bamboo flour's dense adhesive structure could inhibit penetration, reducing joint integrity at higher concentrations. The filler composition determines adhesive properties and bond performance through water absorption, structural interactions, and filler content optimization. These findings emphasize the potential for fine-tuning alternative fillers to achieve desired mechanical performance, ensuring sustainable and efficient plywood production. These findings demonstrate the potential of certain alternative fillers, particularly coconut and lupine flours, excluded from the food value chain, in improving specific properties of plywood. However, further optimization of adhesive formulations and detailed assessments of long-term durability under varying environmental conditions are recommended to harness their benefits entirely. [PERSON] elaborated on the state of the art of hazelnut production and consumption, performed selected measurements, analyzed the data and visualization, and collaborated in writing the first draft of the paper; [PERSON] conceptualization, prepared the literature review, designed the experiments, and performed the experiments, validation, data curation, performed selected measurements, and collaborated in writing the first draft of the paper; [PERSON] conceptualization, resources, supervision, funding acquisition, designing the experiments and performed the experiments, data curation, analyzed the data, analyzed data statistically, reviewed and edited the final version of the paper, project administration.