This standard specifies methods for determining the fineness of flax fibres, including the Fixed Flow rate method and the Fixed Pressure method. Suitable for different types of flax fibres, such as flax combed into hemp, combed into short hemp and hemp strips. Calculate the specific surface area index of the fibres to evaluate their fineness characteristics by measuring the change in resistance or pressure of the fibres under specific air flow conditions. This standard provides an important basis for the quality control of flax fibres, ensuring their performance Stability in Spinning & Weaving and related applications.