## 2 Materials and Methods
### Properties of Sintered Specimens  
After sintering, the mass and the bending properties of at least three specimens per infill pattern and infill degree were measured. The masses of the sintered specimens are shown in Figure 9 to demonstrate how the infill degree and covers affect the mass of specimens. As expected, adding a cover and increasing the infill degree of the specimens increased the mass of the specimens. It can be said that increasing the mass of the specimens increased the maximum flexural stress and flexural modulus. The addition of a cover  
Figure 8: Shrinkage for the various specimens with different infill patterns and infill degrees (**a**) hexagonal 25 to 75%, (**b**) diagonal 50 to 100%, (**c**) linear 0/90 50 to 100%, and (**d**) 100% diagonal and lineal at different angles. profoundly increased the flexural properties of sintered specimens, particularly those with a low infill degree. It had a more pronounced effect than increasing the infill density for specific specimens, agreeing with Steiner's Theorem. For specimens with a 25% hexagonal infill, the maximum stress and flexural modulus increased 166% and 150%, respectively, when adding a cover. When the infill was increased to 50%, adding a cover still increased the stress and modulus, this time by 153% and 130%, respectively. Finally, adding a cover to specimens with a 75% hexagonal infill led to non-significantly different values (Figure 9a). Similar results are observed for specimens with a 50% diagonal infill, where adding a cover increases the maximum stress by 175% and the modulus by 136%. However, adding a cover to specimens with a 75% diagonal infill leads to non-significantly different values (Figure 9b). A slightly different trend was observed when the infill was linear 0/90. In this case (Figure 9c), adding a cover to specimens with a 50% infill increases the maximum stress by 123% and the modulus by 124%; for specimens with a 75% infill degree, adding a cover increases the maximum stress by 121% and modulus by 111%. When comparing specimens with a 100% infill with various patterns, it can be seen in Figure 9d that the mass, maximum stress and flexural modulus are non-significantly different from each other. The results presented in Figure 9 are beneficial when designing lightweight parts. For example, the same bending response was obtained using specimens weighing 9.75 \(\pm\) 0.13 g, 10.38 \(\pm\) 0.22 g or 11.84 \(\pm\) 0.30 g with a hexagonal infill pattern and a cover (Figure 9a). The same bending response was also obtained for specimens weighing 11.77 \(\pm\) 0.49 g, with a 50% diagonal infill and a cover or specimens weighing 13.16 \(\pm\) 0.66 g with a 75% diagonal infill and no cover (Figure 9b). The best absolute bending properties can be obtained by producing specimens with an infill degree of 100%. Nevertheless, the presented results demonstrate the advantages of MEX since hollow specimens with a cover cannot be manufactured by traditional forming or subtractive manufacturing techniques. It would  
Figure 9: Average maximum flexural stress, flexural modulus and mass for sintered specimens with different infill patterns: (**a**) Hexagonal, (**b**) diagonal 45/45, (**c**) linear 0/90 and (**d**) 100% filled with 4 different patterns. also be challenging to produce fully enclosed hollow parts with PBF or BJT since the loose powder is trapped inside the specimens unless a draining orifice is designed in the part. As previously mentioned, increasing the mass of a specimen generally increases the flexural strength and modulus of specimens (Figure 9). This behaviour can be better observed in Figure 10, where the maximum stress and the flexural modulus increase linearly as the mass increases.