We believe that finding out how students think about certain topics that are covered in science classes should not be "the end of the story" but the starting point for planning lessons and designing materials. From this perspective, the research study presented here is intended to explore secondary school (15-18 year old) students' preconceptions of sound attenuation, and of the properties and internal structure of materials. Specifically, we analysed students' explanations for the fact that some materials attenuate sound more than others. This study was conducted within a particular scenario, in which 72 students participated in laboratory sessions aimed at developing students' understanding of the nature, propagation and attenuation of sound. From the analysis of students' explanations, we could identify some conceptions of sound attenuation in materials (e.g. as a result of hindering the entrance of sound, or as a result of capturing sound). The results of this study also indicate that the role of properties of a material and the role of the internal structure that students associate with its acoustic behaviour depend on their conceptions of sound attenuation. We used these results as support for the design of a research-based teaching/learning sequence on the Acoustic Properties of Materials, which is intended to facilitate students' overcoming the specific conceptual difficulties identified in this research study and promote students' development of conceptual models of sound attenuation.