This document specifies the laboratory method for measuring the sound absorption performance of railway noise barriers and related devices acting on airborne sound propagation in reverberant conditions. It covers the assessment of the intrinsic sound absorption performance of devices that can reasonably be assembled inside the testing facility described in EN ISO 354. This method is not intended for the determination of the intrinsic characteristics of sound absorption of noise barriers and related devices acting on airborne sound propagation to be installed on railways in non-reverberant conditions. The test method in EN ISO 354 referred to in this document excludes devices that act as weakly damped resonators. Some devices will depart significantly from these requirements and in these cases, care is needed in interpreting the results.