The use of CF in noise insulation and soundproofing (NISp) applications combines their natural properties, sustainability, and cost-effectiveness, providing an attractive solution for creating quieter and more comfortable environments [1,2,5,6,7,10,12,13,14,15,16,17]. Below is a brief description of the advantages of using foams, particularly those based on CF, for NISp applications. (i) Foams with excellent sound absorption, including CF-based foams, possess a porous structure that effectively absorbs sound waves, reducing noise transmission; the interconnected void spaces in foams allow for the dissipation of sound energy through friction and air resistance [15,16]. (ii) Lightweight foams, including CF-based foams, are easy to handle and install; this characteristic is particularly beneficial for NISp applications as it minimizes additional weight on structures and systems [2,3]. (iii) Sustainable and environmentally friendly, CF-based foams are derived from renewable sources such as wood, making them a sustainable choice; these foams are biodegradable and can be produced from recycled materials, reducing environmental impact [1,4]. (iv) CF-based foams are typically non-toxic and safe for human health; they do not release harmful chemicals or volatile organic compounds (VOCs) into the environment, making them suitable for use in residential and commercial settings [6]. (v) CF-based foams have versatility and adaptability; i.e., they can be easily shaped, molded, or cut to fit various spaces and applications; this versatility allows customized solutions for NISp needs [5]. (vi) In addition to sound insulation, foams have thermal insulation properties, helping to regulate temperature and improve energy efficiency by reducing heat transfer [17]. (vii) CF-based foams can offer cost advantages compared to some synthetic alternatives; their production cost is often lower, making them a cost-effective option for NISp applications [10].

Ultra-light porous materials find significant applications in sound and energy absorption, thermal insulation, radiation shielding, and filtration [18,19,20,21,22]. Another class of materials, namely cellulose-containing materials, has gained attention in foam forming technology. In recent studies [7,8], a lightweight, highly porous, and three-dimensional, shaped, cellulose-based material called foam-paper was introduced. The production process of foam-paper shares similarities with papermaking, but offers several advantages over traditional papermaking techniques: prevention of fiber flocculation, the presence of a three-dimensional porous structure, and reduced water and energy consumption during manufacturing. Foam-paper exhibits versatility and can be applied in various fields such as insulation, packaging, filtration, and acoustics [7,9].

The concept of incorporating foam into the papermaking process was initially proposed by Radvan and Gatward [23] in 1972 and later by Smith and Punton [24] in 1974, with an aim to enhance paper uniformity. Radvan and Gatward [23] utilized foam to prevent fiber flocculation caused by long fibers and high pulp suspension consistency. They introduced the Radfoam process, a foam forming technique employing a discontinuous foam forming unit connected to a small paper machine. Another study on the Radfoam process [25] demonstrated that Radfoam-made sheets exhibit a 20 to 30% higher specific volume (bulk) compared to standard handsheets. In a study by Smith et al. [26] focusing on the structure and characteristics of Radfoam-made materials, it was found that surface tension and bubble spacing within the foam significantly influence the properties of the final product, while chemical effects were deemed insignificant. Tringham [25] and Smith [26] further confirmed that Radfoam-produced material possesses improved uniformity, porosity, and strength. More recently, Al-Qararah et al. [27] from the VTT Technical Research Centre of Finland investigated the impact of various parameters on bubble size distribution in foam-formed cellulose fibers. The study revealed that increasing the rotational speed of mixing led to a decrease in average bubble size and a reduction in air content, resulting in an increased average bubble radius.

In response to the growing demand for sustainable and eco-friendly products, there has been a notable rise in interest in the reintroduction of the foaming process for the development of innovative cellulose-based materials [20,28,29,30,31]. Numerous studies have explored the creation of lightweight porous materials using nanofibrillated cellulose (NFC) through various methods [28,29,30,31].

In latest years, some recent studies also assessed practical aspects of foam-formed composites based on CF for insulation applications. Thus, the main purpose of the study [32] was the identification of physical, chemical, and mechanical properties of soundproofing materials. The review [33] investigated the potential of CF-based polymeric composites for automotive applications, and it concluded that cellulosic (natural) fiber-based polymeric composites offer an efficient alternative to man-made synthetic fibers within the automotive sector. Within their research, Tauhiduzzaman et al. [34] focused on the production of lignocellulosic foams using wood flour or thermo-mechanical pulp (TMP) fibers bound with cellulose nanofibrils (CNFs). Multiscale modelling was proposed to predict the mechanical properties. Hasan et al. [35] have explored various chemical modifications of lignocellulosic fiber to make it more compatible for use as reinforcement in composite materials. In addition, the applications of natural fiber composite were broadly discussed. The study [36] summarized the recent progress within the fields of preparation methods and high-performance cellulose structural material properties. The concluding remarks within the work of Xu et al. [37] suggests that thin layers of sustainable natural materials such as CF can be used to significantly improve the capability of traditional porous media to absorb noise. CF-based materials suitable for filtering, insulation, protective, and hygiene applications can be formed/obtained using aqueous foam as a carrier phase [38,39,40,41,42]. The subtle fiber−bubble interaction provides a very useful tool that can be utilized to alter both structural and mechanical material properties. Indeed, the results within the study by Ketola et al. [38] revealed that there was a clear variation in structure and strength properties between the samples made using different fibers and surfactants. Following the previous idea, the work [43] presents and discusses mechanisms that underlie the formation process, and thus, influence physical properties of formed fiber networks. Another useful conclusion of this work was that the foam rheology is affected by added fibers, which is highly important to the development of foam-forming processes.

Miranda-Valdez et al. [44] concluded that foam-formed cellulose bio-composites are a promising technology for developing lightweight and sustainable packaging materials. Their results showed that organosolv lignin enhances many properties of cellulose bio-composite foams, which are mainly required in practical applications of insulation, packaging, and cushioning. More practically, the paper [45] systematically presents and discusses the technical parameters that can be controlled in practice during foam-forming processes with cellulosic materials, in order to obtain the required properties. The focus of this analysis was on the identification of feasible solutions to compensate for decreased strength, caused by the reduced density and poor water resistance of foam-formed cellulose composites. An innovative foam/natural fiber composite was successfully developed within the work [46]. The authors demonstrated an alternative way to produce composites with promising enhanced mechanical properties. Moreover, the results presented into the study [47] can serve as a basic reference for preparation of highly stable, cellulose-based solid foams, with very good adsorption properties.

Taiwo et al. [48] have proposed an evaluation of the potential of natural fibers for building acoustics absorbers. They have concluded two main ideas: many studies have shown that sound absorbing composites based on natural fibers present good acoustic properties in a high frequency range, similar to synthetic fibers, and natural fibers have been proven as a feasible alternative to synthetic fibers for building acoustic absorbers, thereby alleviating some sustainability issues associated with synthetics.

Cellulose fibers are a natural, environmentally friendly material often used in sound insulation products. However, they do have some negative aspects when compared to other commonly used polymeric materials. Here are some of the drawbacks of using cellulose fibers in NISp applications [36,48,49,50,51,52,53,54,55,56,57,58,59]. (i) Moisture sensitivity, (ii) poor fire resistance, (iii) pest attraction, (iv) settling and decomposition, (v) dust and allergen release and (vi) limited applications mean that CFs may not be ideal for situations where moisture or fire resistance is a critical concern. (vii) While CFs are a natural and renewable resource, their production process may involve the use of chemicals and energy; thus, they have a negative environmental impact. Additionally, the need for fire-retardant treatments can add to the environmental impact. It is important to note that the choice between CFs and synthetic polymeric materials for NISp depends on specific project requirements and priorities, including cost, environmental concerns, and performance criteria.

Within the past 10 years, researchers have focused on CF-based foams, developing and analysing different types, based on various properties of CFs and additives, and optimizing the forming process [45,58,59,60,61,62,63,64,65,66,67], in order to obtain the highest performance for practical applications of noise insulation [58,59,60,64,65,66,67], shock absorption [62], cushioning [45], packaging [45,63], and thermal isolation [61]. The investigations were mainly conducted on experimental tests [45,58,60,61,62,63,64,65,66,67], but computational simulations were also considered [45,59,62,64], modeling potential insulation characteristics compared to widely-used synthetic materials.