Flow Resistivity

Flow resistivity is the resistance a porous material offers to airflow per unit thickness, measured in Pa·s/m². Defined in ISO 9053-1:2018, it is the single most important physical property governing the acoustic absorption performance of porous materials such as mineral wool, glass fiber, and acoustic foam. Optimal flow resistivity for sound absorption depends on the application: values of 5,000–20,000 Pa·s/m² are typical for fibrous absorbers, while excessively high values (above 50,000) make the material surface too reflective and excessively low values (below 1,000) provide insufficient viscous resistance. Flow resistivity is related to fiber diameter, packing density, and material composition. It is a key input for acoustic prediction models including the Delany-Bazley and Miki empirical models, which calculate the complex impedance and absorption coefficient of porous layers from flow resistivity alone. Measurement uses a standardized apparatus that forces a steady airflow through a specimen.