# Advanced Sound Insulating Materials: An Analysis of Material Types and Properties
## 3 Results
In addition, the reviewed articles developed new composite sandwich panels made with flexible polyurethane foam [65], a CCNF/LM aerogel [45], a nanofiber membrane of a composite aerogel [51], and methods for synthesizing composite foams [66], linear and cross-linked polyimide aerogels [67], porous cellulose-based materials with sound-absorbing properties [68], and flexible, superelastic three-dimensional nanofibrous aerogels [52]. The ecological aspects of the materials used has also been analyzed, indicating that natural waste materials such as sheep's wool and sugar cane core have good acoustic properties [44], as do co-fibrous composites combining natural fibers [13]. Other researchers focused on the development of an environmentally friendly, renewable sound absorbing material, the composite aerogel [69]. The articles on polymer properties were the least numerous group. They presented their findings on the acoustic properties of polymer matrix composites (melamine and polyurethane) combined with 316 L stainless steel hollow spheres [22], sandwich panels with flexible polyurethane (PU) foam and nylon-glass grid needle-punched composite fabric (NPUN-G) [65], tungic acid-based biocidal polyurethane foam (TOPUF) [70], and rigid, perforated polyurethane foam panels [71]. The effect of water hyacinth fiber size on the properties of a polyurethane sound-absorbing foam made from recycled palm oil was evaluated [72] and the addition of hollow spheres to polyurethane composites was shown to improve their acoustic properties [23]. The last group consisted of articles related to nanomaterials. The research results presented concern innovative methods for modifying wool fabrics [29], an analysis of the use of porous silica ceramics with good sound absorption properties [73], the development of a porous ceramic composite of reduced graphene oxide and polyvinyl alcohol [60; 74], and the use of silica aerogel in noise attenuation [51; 56; 61]. One study evaluated the properties of polymer composites reinforced with Cissus quadrangularis stem fiber (CQSF) and nanosilica [19] and another investigated the effect of rubber waste powder (RP), graphene nanoplatelets (GnPs) and ground granulated blast furnace slag (GBFS)--material added to concrete to improve its properties--on the acoustic and mechanical properties of rubber concrete [75]. Other studies investigated the properties of jute and coconut fiber composites, a feature of which is the ability to absorb sound [5], as well as a method to incorporate a large fraction of graphene in a styrene-butadiene rubber (SBR) matrix, resulting in nanocomposites with enhanced mechanical properties [76]. Table 1 provides a summary of the publications analyzed covering the years divided into two groups, 2015-2019 and 2020-2024, and the total number of publications in the period. To analyze the statistical correlation between the distribution of different categories and the time periods, a chi-square independence test was applied. In the review of publications on sound-insulating materials presented in Table 1, there is a noticeable increase in the number of publications in the last decade. In the period 2015-2019, 12 papers were published, while in the period 2020-2024, the number increased to 64, indicating a growing interest in this topic in the scientific community. When analyzing the types of materials, the most common materials were fibrous materials (53.95%) and composite materials (36.84%). Porous materials (28.95%) and nanomaterials (14.47%), which can offer new properties and applications in the field of sound absorption, also had a significant share. Polymers, despite their potential, appeared to a much lower extent (7.89%). In terms of the properties analyzed, the publications mainly focused on physical (46.05%), thermal (38.16%), and mechanical (35.53%) properties. Chemical properties were analyzed much less frequently (13.16%).