Exploring Passiflora ligularis Juss. Peel as a Natural Sound-Absorbing and Insulating Material

The need to reduce environmental impact in the construction sector motivates the use of waste-derived materials, particularly in acoustics, where synthetic, non-recyclable products remain predominant. Most conventional acoustic materials rely on fibrous structures, while natural alternatives with non-fibrous internal morphologies remain largely unexplored. This study investigates the acoustic absorption and sound insulation properties of the sweet passion fruit (Passiflora ligularis Juss., also known as granadilla) peel, a natural by-product with a distinctive non-fibrous structure. Samples with thicknesses of 30, 40, and 50 mm were handmade in two variants differing in binder content. Acoustic absorption coefficients (SAC) and transmission loss (STL) were measured using an impedance tube, showing very good results. After verifying normal data distribution with the Shapiro–Wilk test, paired t-tests were applied to assess significant differences in SAC and STL measurements. The 50 mm sample with lower binder content achieved a maximum SAC of 0.98 at 500 Hz. In contrast, samples with higher binder content exhibited superior STL, demonstrating enhanced sound insulation capabilities. Overall, the findings highlight the potential of sweet passion fruit peel as a sustainable acoustic material and illustrate how natural structures that differ from conventional fibrous media can provide competitive and environmentally advantageous acoustic performance.