## 3 Results and Discussion
### Density Results and Microtomography Analysis of Composite Boards  
Figures 1 and 2 illustrate the images of both the reference gypsum or cement board (GB or CB) and the GB/OD@CCF or CB/OD@CCF composite boards, respectively. Table S1 presents the results of density measurements, while Figure 3 illustrates the plotted data against the percentage content of OD@CCF for GB/OD@CCF composites. The data in Figure 3a reveal a slight decrease in gypsum board density with increasing additive content. Specifically, integrating 30% OD@CCF into gypsum boards reduced the density from 0.96 to 0.92 g cm\({}^{-3}\), showing a relatively consistent trend considering the error margins. This decrease aligns with previous findings, as evidenced by the density of the current shape stabilizer, carbon foam, which was recorded at 0.54 g cm\({}^{-3}\)[8], significantly lower than the initial density of the reference gypsum board (0.96 g cm\({}^{-3}\)). Incorporating such lightweight additives contributes to the overall density reduction of the composite boards, although they still satisfy the minimum density criterion of 0.60 g/cm\({}^{3}\) as mandated bythe European standard UNE-EN 13279-1 for gypsum binders and plasters [29; 30]. Similar density reduction trends during additive incorporation have been observed in the literature. For instance, in our prior research [22], adding 30% activated carbon PCM to gypsum boards led to a density decrease from 0.96 to 0.81 g cm\({}^{-3}\). Additionally, [PERSON] et al. [31] noted a density decrease in gypsum boards enhanced with chopped carbon fibers, reaching 1.258 to 1.098 g cm\({}^{-3}\) for a 0.3% volume fraction. Finally, comparing the building boards (GB and CB), the addition of OD@CCF increased up to ~28% of the density of CB, while in the case of GB, the density decreased up to 4% (Figure S3a). To substantiate the findings and investigate the cement and gypsum structure, X-ray computed microtomography (uCT) analysis was carried out, providing vital information on how the addition of various concentrations of additives affects the microstructural properties of the composites. The images on a microscale, as depicted in Figures 4 and 5, highlight unique attributes that change with differing degrees of additive application. In these images, a color scale bar is used to denote the range of X-ray absorption values, which, in turn, represent the different density levels within the wall-board materials, escalating from lower (shown as black) to higher (shown as white) values. The black marks observed throughout these images indicate areas of diminished intensity (air pockets), showcasing the porous nature of the boards. Specifically, in the imagery associated with the cement boards, the CB reference board illustrations predominantly include areas colored in black and purple (refer to Figure 4a). For 10% additive OD@CCF, the microtomography images (Figure 4b) display a reduction in black and purple areas, accompanied by the emergence of new yellow and green areas (higher index components). These areas are more intense in the images of composite boards with higher OD@CCF content, 20 and 30% w.t. (Figure 4c and d, respectively). These latter components likely correspond to OD@CCF particles, indicating their homogeneous integration into the cement board even at the higher loading (30%). These findings are also in agreement with the density measurements, where the density of the cement board increases with increment of OD@CCF loading. Figure 4: X-ray computed microtomography (micro CT) images from CB reference board (**a**) and CB/OD@CCF composite boards with 10% (**b**), 20% (**c**), and 30% (**d**) OD@CCF content. In the case of gypsum boards, the corresponding microtomography images are shown in Figure 5. The images for the GB reference board predominantly feature yellow- and green-colored areas as well as few purple- and black-colored areas (Figure 5a).