What is fibre curvature (crimp) and why does it matter for Australian wool pricing?

Key takeaways

• Fibre curvature describes how strongly a wool fibre bends and is commonly reported in degrees per millimetre. Both OFDA and Laserscan can report it. Woolwise+1

• Curvature correlates with crimp character and contributes to fabric handle, bulk and processing behaviour. PMC

• In Australia, micron, yield, staple length and strength remain the primary price drivers, with curvature influencing demand indirectly via processing performance and style. MSSANZ+1

• OFDA instruments calculate curvature during the same imaging used for diameter, reporting a distribution and mean value for large fibre counts. Woolwise+1

• Standardised preparation matters because curvature is sensitive to handling; clear SOPs improve repeatability across labs and seasons. Woolwise+1
  

Content List

1. Curvature vs crimp in plain English

2. Units, ranges and how labs report curvature

3. Why curvature matters to handle and processing

4. Where curvature fits in Australian pricing

5. How OFDA measures curvature

6. Accuracy, preparation and calibration

7. Practical takeaways for lab managers and growers

8. Summary

9. FAQs

Curvature vs crimp in plain English

Crimp is the visible waviness of a wool staple. Curvature is the underlying measure of how much individual fibres bend. More bend per unit length generally means a higher crimp frequency in the staple, while straighter fibres present lower crimp. The industry uses curvature because it is an objective, instrumented metric that travels well between labs and datasets. Educational material notes there is no reliable subjective appraisal of curvature, so objective reporting is preferred for comparisons over time and between sources. Woolwise

Units, ranges and how labs report curvature

Curvature is recorded as degrees per millimetre. Although the SI unit for curvature is mm⁻¹, the wool industry standardised on degrees per millimetre, and both OFDA and Laserscan report in that unit. In practice, fine Merino lots often show higher average curvature than broader wools, but the exact distribution depends on genetics, environment and preparation. Reference texts also highlight that crimp frequency can indicate curvature but they are not the same measure. Woolwise+1

Why curvature matters to handle and processing

Curvature affects how fibres pack, draft and recover, which in turn influences yarn bulk, softness and fabric comfort. Peer reviewed research links fibre curvature to textile hand and processing efficiency across animal fibres, noting that curvature characteristics shape perceived softness and downstream performance. For specialty blends, studies show lower curvature wools can emulate cashmere-like properties, illustrating how curvature can be used to engineer specific handle outcomes. PMC+1

Where curvature fits in Australian pricing

At auction, clean price is primarily explained by micron, yield, staple length and strength, vegetable matter and related sale parameters. Training and market analyses list those as the main drivers of price formation. Curvature is not usually a stand-alone line in price reports, but it can influence buyer interest by signalling processing behaviour and style within a micron band, so its effects are indirect and contract-specific. For superfine types where handle is paramount, curvature can help differentiate lines that share similar micron and length. MSSANZ+1

How OFDA measures curvature

OFDA instruments calculate curvature from the same image analysis used to measure fibre diameter. During testing, thousands of snippets are imaged and traced; the bending of each snippet over a defined segment is converted into degrees per millimetre and summarised as a distribution and mean. This delivers curvature alongside diameter statistics without a separate run, with IWTO procedures defining the broader frameworks in which OFDA data are used for tops and slivers. Reference bulletins describe curvature as the average amount of bend measured over short fibre segments for OFDA snippets. DOI+3OFDA+3Woolwise+3

Accuracy, preparation and calibration

Curvature is more sensitive to preparation than many other wool metrics. Studies show that differences in core tube geometry and snippet preparation can shift curvature by measurable amounts, even when all else is equal. Earlier investigations also reported that curvature is less stable than mean fibre diameter unless preparation is standardised, which is why labs document SOPs for sampling, scouring, conditioning and slide making. Both OFDA and Laserscan benefit from consistent calibration regimes and reference materials so that curvature and diameter datasets remain comparable across time and sites. AWTA Wool Testing+1

Practical takeaways for lab managers and growers

• Use curvature as a companion to micron when you care about yarn hand, bulk and drafting behaviour, especially for fine spinning and knitwear. PMC

• Treat curvature distributions, not just the mean. Broad distributions can indicate mixed processing behaviour within a lot. Woolwise

• Standardise preparation. Follow documented procedures for scouring, conditioning, snippet making and core sampling to improve repeatability. Woolwise+1

• Align methods to your decision. For tops and slivers where you also need true length distribution with diameter and curvature from the same run, OFDA 4000 under the relevant IWTO method is appropriate. Woolwise

• Be realistic on pricing. Curvature usually contributes indirectly through style and processing performance rather than as a separate line item in Australian auction price models. MSSANZ
  

Summary

Fibre curvature is an objective measure of fibre bend that underpins the visible staple crimp. It is reported in degrees per millimetre by both OFDA and Laserscan and helps explain differences in handle, bulk and processing among lots that share similar microns. In the Australian market, price formation still centres on micron, yield, staple length and strength, and vegetable matter, with curvature influencing demand indirectly through its effect on processing and perceived quality. OFDA calculates curvature during the same imaging used for diameter, providing a distribution and mean for large fibre counts, but careful preparation and calibration are essential because curvature is sensitive to handling. For lab managers and growers, the practical value is using curvature alongside micron to select and position lines for the products and customers you target. Woolwise+4Woolwise+4International Wool Textile Organisation+4

FAQ

What is fibre curvature in wool The objective bend of individual fibres, commonly reported in degrees per millimetre. Woolwise

Is curvature the same as crimp No, crimp is the visible staple wave, while curvature is the measured bending of individual fibres. Woolwise

Does curvature directly set the auction price Not typically; micron, yield, length and strength dominate, with curvature influencing demand via processing and style. MSSANZ+1

Can OFDA report curvature Yes, OFDA reports curvature alongside diameter from the same image analysis. Woolwise+1

Why is curvature sensitive to preparation Sample handling and preparation can shift curvature results, so standardised SOPs are important. Woolwise+1