Wool Fibre Diameter Measurement
topic
Wool fibre diameter is measured on 2 g core-sampled fibre by OFDA100 (BSC Electronics, IWTO-47: 2,000 fibre measurements in 30 seconds, MFD accuracy ±0.5 µm, CV% of diameter distribution), laserscan (CSIRO technology, IWTO-12: 6,000 measurements per test, MFD ±0.3 µm), or airflow (IWTO-6: bulk measurement, MFD ±0.8 µm, fastest but least precise). MFD categories and price premiums at AWEX auction: Ultrafine <15 µm (AUD $40–80/kg clean), Superfine 15.0–18.5 µm ($20–40/kg), Fine 18.6–20.0 µm ($15–25/kg), Medium 20.1–22.0 µm ($10–18/kg), Broad >22 µm ($6–12/kg). Comfort factor CF = % fibres <30 µm diameter: CF >95% required for next-to-skin garments to avoid prickle perception — fibres >30 µm stimulate cutaneous mechanoreceptors at penetration force >0.75 mN (Naylor 1992 threshold). Fibre diameter CV% (intra-lot variability, optimum <20%) and inter-quartile range (IQR <5 µm) indicate lot uniformity — high CV% lots show increased card breakage and yarn CV%. Diameter along staple (OFDA2000 measures MFD at 5 mm intervals along 100+ staples) reveals seasonal fibre diameter variation: nutritional stress causes 'tenderness' zone of 1–3 µm narrowing over 5–15 mm, correlated with staple break position. Instrument calibration: IWTO reference tops (5 certified MFD levels 17–30 µm, issued by IWTO) used daily for OFDA and laserscan instrument verification at accredited wool testing laboratories.
Role
Wool fibre diameter measurement is the single most commercially important textile fibre test globally — the MFD value measured on each wool lot in 30 seconds by OFDA or laserscan determines the price received by sheep farmers, the cost paid by wool traders, and the processing parameters set by worsted mills, making diameter measurement accuracy and inter-laboratory standardisation the foundation of a $3–4 billion annual international commodity market.