Overview
ISO 3343:2010 - Reinforcement yarns - Determination of twist balance index - defines a simple, repeatable test method to measure the twist balance index of folded and cabled reinforcement yarns made from textile glass, carbon, aramid or other reinforcement fibres. The standard specifies specimen selection, the loop-counting principle, conditioning guidance and the format for reporting results. Keywords: ISO 3343:2010, twist balance index, reinforcement yarns, folded yarn, cabled yarn, twist measurement.
Key topics and requirements
- Scope: Applies to folded yarns and cabled yarns of reinforcement fibres (glass, carbon, aramid, etc.).
- Principle: Form an open loop of yarn and count the number of turns the yarn makes on itself and the twist direction (S or Z).
- Specimens: Test on five consecutive specimens taken from the elementary unit or a laboratory sample.
- Specimen preparation:
- Unwind tangentially the first 50 m from the package to obtain a representative length.
- Unwind an additional 1 m for each specimen; do not cut-pinch between thumb and forefinger and let form an open loop with ends held 100 mm apart.
- Counting: Record the number of turns Ni for each specimen and the twist direction; counting may be done while untwisting.
- Result expression: The twist balance index E is the arithmetic mean of the five Ni values, rounded to one decimal place.
- Conditioning/test atmosphere: No conditioning required for routine testing. In case of dispute, perform tests in a standard atmosphere per ISO 291.
- Test report: Must reference ISO 3343:2010 and include sample identification, unwind method, twist balance index and direction, individual specimen results (if required), any deviations or incidents, and test date.
Applications and users
- Who uses it: Test laboratories, yarn manufacturers, composite fabricators, OEMs and quality control teams in aerospace, automotive, marine and industrial composites.
- Practical value:
- Helps ensure consistent yarn twist characteristics for winding, braiding and lay-up processes.
- Assists quality control of reinforcement yarn deliveries and incoming inspection.
- Provides a standardized, repeatable metric for specification, acceptance testing and R&D comparisons.
- Benefits: Simple, low-cost measurement that supports process stability and material traceability in composite production.
Related standards
- ISO 291 - Plastics: standard atmospheres for conditioning and testing (referenced for dispute cases).
- Note: Earlier sampling guidance (ISO 1886) was withdrawn and is no longer referenced in this edition.
This standardized twist measurement method (ISO 3343:2010) is a concise, practical tool for anyone needing a reproducible twist balance index for reinforcement yarn quality and process control.
