Pine (P. pinaster) and quebracho (S. lorentzii) tannin-based foams as green acoustic absorbers

• Open cells tannin–furanic foams give excellent acoustic insulation.
• At frequencies equal and higher than 1000 Hz coefficients of acoustic absorption were 0.7–0.97.
• The acoustic absorption coefficient was lower 0.4–0.6 at lower frequencies (250–500 Hz).
• The thicker is the sample the better is the absorption at frequencies under 1000 Hz.
• The more open cells foams of higher porosity, and lower resistivity perform slightly better.
• The artifice of adding perforations to the foams according to the double porosity concept is not needed for these foams.

Open cells structure tannin–furanic foams prepared using two different types of tannins have been shown to give good sound absorption/acoustic insulation characteristics at medium and high frequencies (1000–4000 Hz) with coefficients of acoustic absorption of 0.85–0.97. Their acoustic absorption coefficient was lower 0.40–0.60 at lower frequencies (250–500 Hz). Compared with commercial foams, tannin–furanic foams have the same typical behavior of light porous materials. The more open-cell is the material the better is its sound absorption. Thicker samples absorb better at medium frequencies for all types of porous material tested.