The open porosity can be directly measured. [Ber42]

Schematic representation of an acoustical porous medium.
The fluid phase, in white, is made up of a network of connected pores.
The closed pores are considered to be a part of the solid phase, in black.
The modelization of visco-thermal dissipative effects added with dead-end pores is a work in progress.

Range of values

For acoustical materials, its range of values goes from less than 0.01 for facings or [micro-] perforated panel (MPP) is approximately [0.70 0.99].