## 1 Introduction
Although inexpensive acoustic materials can be found on the market, in disadvantaged contexts they can not be easily purchased because people have little or no financial resources. An alternative can be the realization of no-cost panels featuring acoustic properties. While on the one hand there is growing attention to the well-being of people, on the other it is necessary to define actions aimed at protecting the environment, optimizing the system that provides us with the raw materials necessary to make the products, and which houses the waste. To lighten the load on the environment, it is necessary to use raw materials in a conscious way, for example, by extending the life of the products as much as possible. Additionally, since many materials still possess exploitable properties when they are discarded, they can be reused for other purposes. This model is called Circular Economy (CE) which is in contrast to the linear economy model. In the linear economy model, the raw material is extracted, processed to make the product that, at the end of its life, is discarded. The circular economy model, on the other hand, is based on the 7R principle: reduce, reuse, recycle, repair, replace, recovery, remanufacture as shown in Figure 1.  
With a view to the circular economy and sustainable cities, household end-of-life materials (EoLHM), such as clothes or packaging, could be reused to realize acoustic panels. EoLHM can be defined as household waste materials which still possess exploitable properties, thus making them suitable for reuse. Many EoLHM still have properties when discharged and are largely available: for example, the estimated yearly global production is about 241 million tons for cardboard and paper packaging [10; 11], 380,000 million tons for plastic packaging [12], and 92 million tons for textile waste [13] of which only the 12% is recycled [14]. The large availability of EoLHM and the problems related to recycling can support the approach of converting them into acoustic panels: as suggested in [15], this avoids the generation of waste, reduces the footprint due to raw materials extraction, and makes them accessible also to vulnerable population that can not afford commercial acoustic materials. Moreover, since EoLHM are largely available, this approach could incentive buildings renovation and facilitate the achievement of the energy and environmental international goals set by the European Parliament [16; 17]. The study presented in this paper explores the possibility of converting EoLHM into panels featuring interesting acoustic properties, and it is focused mainly on those EoLHM that can be reused without any type of processing so that they are directly available to low-income households. Indeed, any treatment would entail costs that would affect end-users and, consequently, the vulnerable population may not be able to afford them. Specifically, the aim of the experimental analysis presented in this paper is to understand which EoLHM can be used to make acoustic panels of limited thickness, and how these materials can be assembled to meet both sound insulation and sound absorption requirements. Since the panels are intended for the most disadvantaged population, they must be easy to be assembled and installed, so that these people, once trained, can collect the necessary EoLHM and assemble the panels independently. The first part of the study addresses the state of the art regarding the reuse of EoLHM to realize acoustic panels. There are several studies in the literature that address the recycling of these materials, but only a limited number analyzes their possible reuse. This highlights that the approach proposed in this paper is quite innovative. In the second part of the paper, EoLHM suitable for low-cost acoustic insulation panels for indoor comfort improvement are investigated by means of experimental tests performed with a 4-microphone impedance tube technique. Five sets of samples have been tested. In the first set of samples, the acoustic performance of egg-cartons has been evaluated.