<p>Acoustic behavior is one of the main properties in porous materials. A significant feature of the absorption coefficient spectra is the first absorption peak, as its frequency indicates the onset of high absorption. This work examines the variation in global absorption, as well as changes in the maximum absorption coefficient and its frequency with respect to material thickness. Absorption coefficients were measured using an impedance tube for 157 samples of four types of porous absorbers. Statistical analysis revealed significant differences among the sample groups. A saturation effect was observed in overall sound absorption. Additionally, the magnitude of the first peak increased with thickness for Foam and PET, but decreased for Butts-derived materials. The frequency of this first maximum also showed differences across sample types and in comparison with the theoretical value. Among the materials studied, samples derived from cigarette butts demonstrated the best acoustic performance.</p>