Biomaterials derived from plant waste are becoming a major topic of research as substitutes for conventional thermal insulating materials. However, many of these materials lack acoustic studies to evaluate their performance. The objective of this study is to assess the acoustic behaviour of four different biomaterials, bound with two different types of natural binders, and to perform a comparison between them. The materials under study are rice husk, rice straw, sunflower stalk, and Posidonia oceanica. The selection of these materials was based on their local availability and ease of procurement, as well as previous comparisons with other accessible materials. The bio-binders used are xanthan gum and arabic gum, chosen for their good results in binding these materials. Before conducting the acoustic tests, a physical characterization of the materials was carried out, along with a thermal conductivity test to evaluate their performance as thermal insulators. The acoustic tests performed were the acoustic absorption tests conducted using the Kundt’s tube method. For this, samples of each material were prepared in varying thicknesses, and the thickness yielding the best result was tested again. The results provide an initial understanding of the acoustic performance of these materials, as well as a comparison between them.