A new model for predicting the acoustical properties of fibrous materials, the characteristic impedance Zc and the propagation constant γ, only from their airflow resistivity was constructed. The Delany-Bazley and Miki models are well known as conventional prediction methods. Their formulas are similar, and their difference is in the values of coefficients and degrees in the formulas. In this research, the acoustical properties and airflow resistivity of fibrous materials, 15 types of glass wool and 9 types of rock wool, were measured and compared with values obtained by conventional methods of prediction. It was found that the introduction of an expression involving the common logarithm improved the conventional models. This new model is more effective than the conventional models, particularly for the prediction for high-density fibrous materials where f⁄σ<0.01 m³/kg and low-density ones where f⁄σ>0.1 m³/kg.