## 4 Discussion
An investigation into the effects of the geometry and filling level of glass dispersion particles on the optical and mechanical characteristics of flexible high-transmission composites based on thermoplastic polyurethane (TPU) showed that adding any filler reduced the tensile strength while increasing the elastic modulus of the composite material [73]. So, the response of TPU upon the addition of glass particles differs from the findings presented herein. Glass spheres, glass flakes, and milling glass fiber were some of the fillers utilized. Notably, the material's yield strength increased significantly as a result of the addition of glass flakes and the milling of glass fiber [73]. Additionally, glass fiber (GF) is frequently utilized in polylactic acid (PLA) composites as a reinforcing material, but not for MEX 3D printing so far. The mechanical properties of PLA composites are significantly enhanced by the addition of glass fiber, with an approximately 40% improvement. The glass fiber reinforcement acts as a crystallinity-promoting nucleating agent for the composites [74]. Such results agree with the findings of the current study, in which a 33.8% increase in the tensile strength of PLA/Glass Flakes 6 wt.% compared to the unfilled PLA polymer was achieved. The examined composites' mechanical and thermal properties have significantly improved as a result of the addition of glass fillers, such as glass beads, glass flakes, and glass powder. The inclusion of glass fillers has improved various mechanical properties while preserving or even increasing tensile strength and stiffness. Additionally, the glass fillers have demonstrated positive benefits on the composites' thermal stability, with variations depending on the filler's form and concentration [74]. Overall, the use of glass fillers as reinforcement agents has been successful in improving the composites' overall performance, opening up possibilities for further study and prospective applications in a variety of industries. It is also crucial to point out that incorporating glass particles into the PLA matrix to strengthen the polymer's strength during the production of 3D parts does not result in a significantly higher cost. It should be noted, nevertheless, that the use of three different kinds of glass particles came at an added cost. The price of the raw material needed to prepare PLA (polylactic acid) is approximately EUR 5 per kilogram or EUR 0.005 per gram. The price increases to about EUR 20 per kilogram after this raw material is processed and turned into industrial filament. The cost of the raw materials required to create the filament is approximately one-fourth of the final cost of the filament, which supports the price disparity. The price of the three types of glass particles (beads, flakes, and powder) for laboratory-scale research is approximately EUR 0.4-0.5 per gram. Consider the 3.0 wt.% glass beads compound, which demonstrated the greatest increase in the mechanical response, as an example. In order to add 3.0 wt.% of glass beads to the PLA matrix, additional raw material expenses must be incurred, which are estimated as EUR 0.5/g (the cost of the glass beads) times 0.03 (3.0 wt.%). As a result, the glass bead reinforcing incurs an additional cost of EUR 0.015/g. Since the composite is reinforced with 3.0 wt.% glass beads, the overall cost per gram rises from EUR 0.005/g for pure PLA to EUR 0.02/g. It is important to note that when switching to industrial-scale utilization, this price can be considerably lowered. Economies of scale are advantageous for industrial-scale production and can result in decreased material prices, including glass particles.