ISO 1973:2021

Overview

ISO 1973:2021 - Textile fibres - Determination of linear density - Gravimetric method and vibroscope method - specifies two laboratory methods for measuring the linear density (mass per unit length, typically expressed in decitex) of textile fibres. The standard covers:

• A gravimetric method for bundles (average linear density of a bundle of fibres).
• A vibroscope method for individual fibres (measurement of single-fibre fineness and distribution).

The standard is applicable mainly to fibres that can be kept straight and parallel and are readily freed of crimp. It is well suited to man‑made fibres (and usable with less precision on natural fibres). It does not apply to tapered fibres; the vibroscope method may be unsuitable for hollow or flat (ribbon‑like) fibres.

Key topics and technical requirements

• Scope & limitations: Applies to bundles (gravimetric) and individual fibres (vibroscope); excludes tapered fibres and has restrictions for hollow/flat fibres.
• Sampling & atmosphere: Sampling per ISO 1130; conditioning and testing atmospheres per ISO 139.
• Gravimetric method:
  • Prepare combed, parallel bundles; typical test bundles comprise 50 fibres (increase to max 500 if required for weighing accuracy).
  • Use a balance with accuracy of at least ±1%.
  • Cut specimens under controlled tension and weigh to determine average linear density.
• Vibroscope method:
  • Measures resonance frequency, vibrating length and applied tensioning force to compute linear density.
  • Vibroscope accuracies required: tension ±0.5%, frequency ±0.5%, length ±1%.
  • Typical tensioning force guidance: around 0.6 ± 0.06 cN/tex (adjust to remove crimp without stretching).
  • Validation step: compare vibroscope readings against gravimetric results (e.g., 100 fibres) and apply a correction factor if relative difference > ±3% (by agreement of parties).
• Reporting: Mean values, statistical distribution (for vibroscope), and test conditions must be documented.

Applications and users

ISO 1973:2021 is used by:

• Textile testing laboratories and quality control teams
• Fibre and filament manufacturers
• R&D and process engineers concerned with yarn spinning, nonwovens and downstream processability
• Certification and compliance testing bodies

Practical benefits include reliable determination of fibre fineness (average and distribution), which supports process optimisation, product specification and quality assurance.

Related standards

• ISO 139 - Standard atmospheres for conditioning and testing
• ISO 1130 - Sampling of textile fibres for testing
• ISO 6989 - Length and length distribution of staple fibres (single‑fibre measurement)

Keywords: ISO 1973:2021, linear density, gravimetric method, vibroscope method, textile fibres, decitex, fibre testing, textile standards.