The purpose of this work is to create and examine the mechanical properties of an eco-friendly, low-cost natural fiber filled with glass-fiber-reinforced polymer composite. Cotton shell (CS) particles are a less expensive natural fiber material that can be used as filler, integrated with glass fiber in epoxy-resin matrices. By keeping the optimized resin weight as a constant (75 % of mass fractions), six composites C1, C2, C3, C4, C5 and C6 of different weight percentages of glass fiber and the CS filler were prepared and the corresponding mechanical properties were examined as per ASTM standards. The glass fiber of 15 % of mass fractions and filler material of 10 % of mass fractions of the composite "C3" shows the best mechanical properties. The mixture design analysis is used to evaluate the results obtained mathematically, and the predicted values confirm that the 10 % of mass fractions of addition of CS particles with the glass fiber augment the mechanical properties of the hybrid composites. The chemical composition of the cotton shell particles was analyzed by using energy-dispersive spectroscopy (EDS). Also, the surface morphology of the raw CS particles and the fractured surfaces of the tested specimens were examined with a scanning electron microscope (SEM). Keywords: E-glass fiber, cotton shell (CS) particles, epoxy resin, mechanical properties, mixture design analysis Namen tega dela je bil oblikovati in preiskati mehanske lastnosti cenenega, ekolo{ko prijaznega polimernega kompozita iz naravnih vlaken ter oja~anega s steklenimi vlakni. Delci bomba`nih lupinic (angl. CS) so cenen vir naravnih vlaken, ki se lahko uporabi kot polnilo in s steklenimi vlakni integrira v epoksidno matrico. Avtorji~lanka so v tej raziskavi obdr`ali konstantni masni dele`epoksidne smole (75 mas. %) v {estih me{anicah C1,C2,C3,C4,C5 in C6 z razli~nimi masnimi dele`i steklenih vlaken in CS polnila. Pripravljene kompozite so mehansko okarakterizirali v skladu z ASTM standardom. Kompozit C3 s 15 mas. % steklenih vlaken in 10 mas. % CS polnila je imel najbolj{e mehanske lastnosti. Da bi matemati~no ovrednotili dobljene rezultate so avtorji uporabili t.i. MDA (angl.: Mixture Design Analysis) in napovedane vrednosti analize so potrdile, da dodatek 10 mas. % CS delcev k steklenim vlaknom, izbolj{a mehanske lastnosti hibridnih kompozitov. Kemijsko sestavo bomba`nih lupinic so analizirali z energijskim dispezijskim spektrometrom (EDS). Prav tako so povr{insko morfologijo CS delcev in prelomne povr{ine preiskovanih vzorcev pregledali z vrsti~nim elektronskim mikroskopom (SEM).