# Advanced Sound Insulating Materials: An Analysis of Material Types and Properties
## 3 Results
Table 3 shows an analysis of publications on different types of sound-absorbing materials (composite, fiber, polymer, porous, and nanomaterials) in relation to the properties studied and the research methodology used. A total of 76 papers were published in the analyzed period, most on fibrous materials (41 publications) and composite materials (28 publications), much less on porous materials (22 publications), nanomaterials (11 publications), and polymers (6 publications). Research was most often focused on physical (35 publications) and thermal (29) properties, and, to a lesser extent, on mechanical (27) and chemical (10) properties. The physical properties of fiber and composite materials were particularly frequently analyzed. The vast majority of studies were carried out experimentally (71 publications), while literature analyses (23) and conceptual studies (21) were much less frequent. The largest number of experimental studies focused on fiber and composite materials. The chi-square test values for the associations between material types and properties (\(\chi^{2}=13.63\); \(p=0.33\)) and the research methodology (\(\chi^{2}=13.14\); \(p=0.11\)) are presented in Table 3, which indicates that there were no statistically significant relationships between material types and the choice of methodology (\(p>0.05\)), but there are some trends worth noting. Based on the data presented in Table 3, clear trends can be observed in the choice of research methodology depending on the type of material analyzed. Composites are  
\begin{table}
\begin{tabular}{l l l l l l l l} \hline \hline
**Name** & **Composites** & **Fibrous** & **Polymers** & **Porous** & **Nanomaterials** & **Total** & **Chi-square** \\ \hline Total & 28 & 41 & 6 & 22 & 11 & 76 & \(\chi^{2}\) \\ \hline Material properties & & & & & & & \\ \hline Chemical & 2 & 5 & 0 & 4 & 2 & 10 & \\ Mechanical & 15 & 10 & 5 & 5 & 4 & 27 & \(\chi^{2}=13.63\) \\ Physical & 12 & 19  
characterized by a strong predominance of experimental research--as many as 25 out of 28 publications in this category are based on experimentation, with literature analysis and conceptual approaches being used to a much lesser extent. Fiber materials are also preferred for experimental research (38 of 41), but there is also a noticeable presence of conceptual methodology (12 publications), indicating a more diverse research approach in this group. In the case of polymers, all publications (six) are purely experimental, indicating a clear choice of this research method in the context of this material. Porous materials, on the other hand, are distinguished by a relatively high proportion of conceptual approaches--up to 11 of 22 publications--with a significant proportion of experiments (21), which may indicate the search for a new theoretical research framework for this category of materials. With regard to nanomaterials, the experimental methodology dominates (11 out of 11), but conceptual (4) and review papers (2) also appear, indicating that complementary approaches are being developed. In summary, experimental methodology is by far the most commonly used in all types of materials, especially polymers and composites. However, in the case of fibrous and porous materials, a greater diversity of research approaches can be observed, with a clear contribution of conceptual methods and literature analysis. This suggests that the choice of methodology may be partly dependent on the characteristics of the material in question and the extent to which it is known in the scientific literature. Figure 6 shows the number of publications per type of sound-absorbing material. The dominance of fibrous and composite materials is evident, together accounting for the majority of all studied. Among the material properties, the physical and thermal characteristics were investigated most frequently, especially with respect to fibrous materials. In turn, the research methodology shows a clear advantage of experimental approaches over literature and conceptual analyses, regardless of the material type.