_applied sciences_  
_A Article_  
**Glass Fillers in Three Different Forms Used as Reinforcement Agents of Polylactic Acid in Material Extrusion**  
**[PERSON] 1, [PERSON] 1,*\(\copyright\), [PERSON] 1\(\copyright\), [PERSON] 2, [PERSON] 1\(\copyright\), [PERSON] 1 and [PERSON] 1**  
Footnote 12: foot  
response of the 3D-printed products compared to the respective injection-molded ones [16]. Fiber-reinforced polymers (FRP) are materials that were developed by the polymer industry to increase the structural durability of traditional composites [17]. Fiber-reinforced composites prepared, utilizing additive manufacturing (AM), have been found to have problems with porosity or air bubbles. The fiber-matrix bond is weaker when there is porosity, which reduces the composite's overall strength [18; 19; 20]. Research has suggested several approaches to address this issue, such as employing expanding microspheres as fillers [19] or flake or particle reinforcement rather than chopped fiber reinforcement [20]. These techniques have demonstrated success in lowering the porosity levels to under 10% [16]. Numerous studies have been published regarding the creation of composites reinforced with fibers. For example, [PERSON] et al. [21] added chopped glass fibers to ABS polymers using MEX 3D printing technology to increase the tensile strength of the finished product. According to the research, the bridging effect produced by the fibers crossing between layers led to an increase in interlayer bonding strength as the number of fibers grew [16; 21]. It was also discovered that adding glass fibers to an ABS filament considerably increased its strength, albeit at the expense of decreased flexibility and handling properties [21]. In another investigation, carbon, Kevlar, and glass fiber nylon composites were created, and the mechanical characteristics of each type of composite were examined. The study concluded that this technology has significant potential for further development, which may result in the creation of composite materials that are currently unattainable [16]. Glass is one of the first and best-known high-performance fibers [22]. Since the 1930s, it has been utilized to produce fiber [23]. In general, fiberglass is a generic term used to describe plastics reinforced with glass fibers. Depending on the intended use, several varieties of glass can be used to create glass fibers [24]. Particularly, in comparison to other fibers, fiberglass is a material that is lightweight, sturdy, and less brittle. Its main benefit is that it can be shaped into complex designs, which is why it is frequently used in products, such as bathtubs, boats, airplanes, roofing, and many other things [25]. Glass fiber-reinforced concrete (GFRC) has been a major contributor to the economics, technology, and aesthetic of the global building industry for more than 40 years now [25; 26]. In this study, glass was used as a reinforcement agent in a PLA matrix in three different forms: beads, flakes, and powder. Glass flakes are a high aspect-ratio reinforcing additive with several industrial uses, such as in fire protection [27] and in denuture applications [28]. It is made of modified 'C' glass and is available in three thickness ranges: 3.5-5.5, 1.9-2.5, and 1.4-1.9 \(\upmu\)m [28]. Glass flakes are also available in three different particle size distributions: unmilled, milled, and micronized. Producers of glass flakes assert that adding glass flakes to specific thermoplastics has significantly enhanced planar reinforcement and flexural modulus [28]. The addition of glass beads also significantly improved the stiffness and strength of the materials in fiber-reinforced laminated polymer bulk composites. The glass beads' rigidity, which made it easier for the load to be transferred from the matrix to the fiber reinforcements with efficiency, was credited for this improvement [28]. The glass beads' spherical form and micro-scale diameter make them effective in preventing crack progression [29; 30; 31; 32].