A novel low-frequency anechoic lining for use underwater is investigated both theoretically and experimentally. Measurements are made in an impedance tube. The reflection coefficient of any lining material placed at the end of the tube can be found from the real part of the input mobility. The results are compared with theoretical predictions. The experimental results agree qualitatively with the theoretical predictions and any quantitative discrepancy is probably due to inaccuracies in manufacturing the anechoic lining itself, rather than in the measuring technique used or in the theoretical model.