## 3 Results and Discussion
### Water Resistance Performance  
Figure 6 presents water absorption behavior for control PUR foam and PUR foam composites with each type of filler at concentrations ranging from 2.5% to 10%. Water absorption at each concentration of filler is presented separately to highlight the impact of each filler type on the parameter more clearly. Considering the concentration of each filler type, a reduction in water absorption is noted for Per and Verm fillers. The parameter is reduced by 15% at 2.5 wt.% Per filler concentration (Figure 6a). The further addition of Per increases water absorption, but it remains 7.5% lower than control PUR foam (Figure 6b-d). It can be explained by the fact that Per does not absorb much water. On the contrary, it holds water within the tiny crevices that pockmark its surface [61]. Additionally, the obtained water absorption results correlate with the closed-cell content for PUR/Verm composites, as shown in Table 3.  
A similar but slightly more intense tendency is observed for Verm filler-modified PUR foam composites. The incorporation of 2.5 wt.%, 5 wt.%, and 7.5 wt.% Verm by 15%, 5%, and 5%, respectively, decreases water absorption compared to the control PUR  
Figure 6: Comparison of short-term water absorption by partial immersion of PUR foam composites with different fillers at **(a)** 2.5 wt.%, **(b)** 5 wt.%, **(c)** 7.5 wt.%; and **(d)** 10 wt.%. foam (Figure 6a-c). However, a further 10 wt.% Verm deteriorates the parameter by 2.5% compared to control PUR foam (Figure 6d). It is well known that expanded Verm absorbs water like a sponge whether it is used in polymer composites, cement-based composites, or mortars [62; 63]. Its flakes expand when it sops up water. This means that structural damage occurs. For instance, Table 3 shows that incorporating Verm in any concentration reduces the number of closed cells, which may also contribute to the deterioration of moisture-related properties. Dex-activated Per (PerDex) fillers show a decreasing tendency in water absorption values, even at a maximum addition of 10 wt.% PerDex (Figure 6d), PUR foam composites exhibit \(\sim\)18% lower water absorption than control PUR foam and \(\sim\)11% compared to untreated Per filler. However, Dex-activated Verm (VermDex) filler positively impacts the parameter at only up to 5 wt.% addition (Figure 6b,c), i.e., maximum by \(\sim\)13% compared to control PUR foam and by \(\sim\)8% compared to unmodified Verm. Further incorporation of this filler up to 10 wt.% deteriorates the resistance to water by a maximum of 5% compared to control PUR foam and by \(\sim\)3% compared to unmodified Verm (Figure 6c,d). As indicated in FTIR spectra of VermDex (Figure 2), Verm activation with Dex allows the formation of Dex-Si-O-Si-Dex linkages, which inhibit the filler's participation in further reaction with isocyanate to form a strong interface between filler particles and polymer matrix. On the contrary, PerDex filler has hydroxyl groups, which only partially react with silanols in Per. Therefore, participation in the reaction during PUR foam composites synthesis is not entirely restricted, thus allowing the formation of a more reliable interface between particles and PUR foam composites. Therefore, the FTIR spectra of control PUR foam and PUR foam composites with Dex-activated fillers are presented in Figure 7.  
It can be seen that all PUR foam composites have similar patterns. The intensity at 3320 cm\({}^{-1}\) is assigned to the stretching band of N-H. In addition, asymmetrical and symmetrical vibrations of C-H take place at wavenumbers of 2922 cm\({}^{-1}\) and 2853 cm\({}^{-1}\), respectively. Furthermore, unreacted N=C=O groups are observed at 2365 cm\({}^{-1}\), indicating  
Figure 7: FTIR spectra of PUR foam composites with (**a**) Per and PerDex and (**b**) Verm and VermDex. the excess of isocyanate used in the synthesis of the control PUR foam and PUR foam composites.