<p>Glass fiber is an inorganic reinforcement material widely used in rubber-based technological products. This study investigates the properties of natural rubber/glass fiber composites, focusing on their potential to enhance mechanical performance while reducing costs. A series of tests were conducted to evaluate the rheological, mechanical, swelling, and morphological characteristics of the investigated natural rubber composites. Quantitative analysis showed that the composition containing 16 phr glass fiber resulted in a 59.5% increase in tensile strength compared to composites filled with traditional fillers such as sodium bentonite, calcium carbonate, silica, and calcined kaolin. The composite also showed a significant boost in mechanical properties, with notable increases in modulus at 100% and 300% strain, strain energy, and a stronger Payne effect, which indicates strong interfacial adhesion, as confirmed by morphological analysis. Morphological analysis of fractured surfaces confirmed excellent adhesion between glass fiber and natural rubber. Notably, the natural rubber/16 phr glass fiber composite exhibited exceptional swelling resistance in toluene, with a quantifiable reduction in swelling compared to other composites. This makes it suitable for automotive interiors. Cytotoxicity tests verified that the material is non-toxic, supporting its use in human-related applications. These results suggest that glass fiber is a better and more sustainable reinforcing filler for enhancing the performance of rubber products in the automotive industry.</p> Graphical Abstract <p></p>