## 3 Results and Discussion
### Mechanical Performance
The F-criterion statistic is 0.51, \(p\) = 0.63, and R\({}^{2}\) = 0.145. Moreover, the statistical analysis of compressive strength of PUR foam composites with 7.5 wt.% different fillers showed (Figure 10c) that there were no differences between the PUR/PerDex-7.5 and PUR/VermDex-7.5 foam composites. The F-criterion is 0.57, \(p\) = 0.49, and R\({}^{2}\) = 0.125. When comparing the PUR/PerDex-7.5 and PUR/VermDex-7.5 foam composites with the control PUR, the analysis showed that there is no difference between the average values. The F-criterion is 0.51, \(p\) = 0.63, and R\({}^{2}\) = 0.146. However, the significant differences are observed between control PUR, PUR/PerDex-7.5, and PUR/VermDex-7.5 and PUR/Verm-7.5. Lastly, the statistical analysis of the compressive strength of PUR foam composites with 10 wt.% different fillers showed (Figure 10d) that there are significant differences between compressive strength of all PUR foam composites compared to the control PUR. The F-criterion is 164, \(p\) = 0, and R\({}^{2}\) = 0.985. Furthermore, Figure 11 presents the tensile strength results of control PUR foam and modified PUR foam composites. For PUR/Per and PUR/Verm foam composites with filler concentrations of 2.5-5 wt.%, no significant changes in tensile strength are observed, indicating that these fillers do not deteriorate the parameter at lower concentrations. However, PUR/Per-7.5 and PUR/Per-10 foam composites showed a 25% and 22% decrease in tensile strength compared to the control PUR foam, while PUR/Verm-7.5 remained unchanged, and PUR/Verm-10 had a 5% higher tensile strength compared to the control PUR foam. It seems that Per filler has a higher negative impact on tensile properties. Additionally, both fillers were found to be inefficient under compression and tension loads. However, different tendencies can be seen for PUR foam composites with Dex-activated Per and Verm particles. The highest tensile strength for PUR/PerDex foam composites is observed at a 2.5 wt.% PerDex concentration. The parameter increased by 34% compared to the control PUR foam, although further addition of PerDex filler deteriorated the parameter. However, compared to the control PUR foam, the tensile strength remains higher, up to 7.5 wt.% PerDex concentration. Smaller and more uniform cell sizes and wall thickness (Table 3) enhance tensile strength. A finer cellular structure provides a larger surface area for stress distribution, preventing localized failure. Such an effect is related to improved interfacial adhesion associated with the PerDex surface. [PERSON] et al. [67] reached a similar conclusion when modifying flexible polyurethane foam with potassium peroxide-oxidized tire rubber. Even though the cells of PUR/Per-10 foam composite are smaller, the destruction of microstructure at higher loading of PerDex filler takes place as indicated, as can be seen in Figure 5g. Therefore, a 22% reduction in tensile strength (Figure 11d) at 10 wt.% PerDex addition can be seen. Moreover, a slightly different conclusion can be made for PUR/VermDex foam composites. The tensile strength of these PUR foam composites at any loading of VermDex filler increased, and the highest parameter was 26% higher than that of the control PUR foam composite. The presence of Dex on the Verm surface might be creating stronger interactions with PUR chains. This enhances interaction and allows for more efficient stress transfer from the PUR matrix to stronger VermDex particles when the foam composite is under tensile stress. The statistical analysis of the tensile strength of PUR foam composites with 2.5 wt.% different fillers showed (Figure 11a) that there are no differences between the PUR/Per-2.5, PUR/Verm-2.5, and PUR/VermDex-2.5 foam composites. The F-criterion is 0.49, \(p\) = 0.64, and R\({}^{2}\) = 0.139. When comparing the PUR/Per-2.5, PUR/Verm-2.5, and PUR/VermDex-2.5 foam composites with the control PUR, the analysis showed that there is no difference between the average values of tensile strength.