Tex (tex): Linear Mass Density for Fibres and Filaments

Definition and Relationships

Linear mass density fundamentals

Tex quantifies mass per unit length. Mathematically, tex = (m / L) × 10³, where m is mass in grams and L is length in metres. A yarn weighing 25 g over a length of 5,000 m has tex = (25 / 5,000) × 10³ = 5 tex. Because tex uses grams and kilometres, it directly ties to SI base units of mass and length. Submultiples include decitex (dtex, g per 10,000 m) and millitex (mtex, g per 1,000,000 m). Converting between tex and denier relies on denier = 9 × tex, while tex equals 0.1 g per 100 m, a convenient format for laboratory conditioning tests.

Cross-sectional properties and density

Tex links mass to cross-sectional geometry and material density. For a fibre of radius r and material density ρ, the theoretical tex equals tex = ρπr² × 10³, assuming a circular cross-section and homogeneous composition. Hollow fibres, trilobal profiles, or polymer blends require adjusted area calculations. Designers compare measured tex with theoretical predictions to evaluate polymer draw-down, void content, and moisture uptake, tying into density concepts explored in the density article.

Historical Development

From denier to tex standardisation

Early textile industries used denier and worsted count systems, which varied by region and fibre type. Post–World War II international trade expansion prompted the International Organization for Standardization (ISO) and the Bureau International pour la Standardisation des Fibres Artificielles (BISFA) to promote tex as a universal unit. ISO 1144 and ISO 1139 codified tex-based numbering for filament and spun yarns, enabling consistent communication across manufacturers. Today, most technical textiles specify linear density in tex or dtex, even when denier remains familiar in apparel markets.

Integration with quality assurance systems

Textile mills integrate tex measurements into statistical process control. Automated winders and draw frames capture continuous mass-per-length data, triggering alarms when deviation exceeds set tolerances. Standards such as ISO 2060 describe the skein method for measuring tex, while ISO 2062 covers tensile testing using tex to normalise specific strength (cN/tex). Quality certifications including OEKO-TEX® and ISO 9001 require documented calibration of balances and length measurement devices traceable to SI units.

Measurement Concepts

Conditioning and sampling

Fibre moisture content affects mass; therefore, ISO 139 prescribes conditioning (65 % relative humidity, 20 °C) before tex measurement. Samples should represent production lots, combining bobbins from multiple positions to capture variation. For staple yarns, skein winding devices produce a known length, which is weighed to compute tex. Filament yarns may employ capacitance or optical sensors for online monitoring, calibrated against gravimetric methods.

Instrumentation and calibration

Precision balances with readability to 0.1 mg support low-tex measurements, while length meters ensure ±0.1 % accuracy. Calibration weights traceable to the kilogram and length tapes certified against metre standards maintain measurement integrity, echoing practices described in the mass realisation article and the length guide.

Data analysis and process control

Mills calculate coefficient of variation (CV%) for tex to monitor uniformity. High variability may stem from drafting faults, inconsistent polymer viscosity, or temperature fluctuations in spinning rooms. Integrating tex data with tensile results (cN/tex) yields specific tenacity, a key performance indicator for high-strength fibres. Statistical software alerts operators to trends before fabric defects arise.

Applications Across Industries

Apparel and technical textiles

Apparel designers select tex to balance drape, opacity, and durability. Lightweight fabrics may use yarns below 20 tex, while denim and upholstery require higher tex for strength. Technical textiles—including airbags, geotextiles, and parachutes—rely on tightly controlled tex to meet performance specifications. The yarn length calculator helps translate spool mass into coverage for knitting or weaving plans.

Composites and additive manufacturing

Carbon fibre prepregs list tex to describe tow size (e.g., 12k tow at 800 tex). Engineers use tex to compute fibre volume fraction and resin requirements. In fused filament fabrication, polymer filament tex influences extrusion rates, bead width, and part density. Estimation tools like the 3D print time & cost calculator assist with planning material consumption and production schedules.

Filtration, medical, and sustainability applications

Air and liquid filtration media rely on fibre tex to balance pressure drop and capture efficiency. Designers align tex with pore size targets and use the air changes per hour calculator to evaluate HVAC performance impacts. In medical sutures and vascular grafts, tex determines handling characteristics and tissue integration. Recycling initiatives quantify tex to sort textile waste streams and calculate mass yield from recovered fibres, supporting circular-economy metrics.

Importance and Future Outlook

Digitalisation and Industry 4.0

Smart spinning frames collect tex data in real time, feeding digital twins that simulate production scenarios, predict breakage, and optimise quality. Machine learning models correlate tex variations with process parameters such as draw ratio, melt temperature, and take-up speed, enabling predictive adjustments. Automated reporting ensures compliance with customer specifications and certification requirements.

Sustainability and resource efficiency

Precise tex control minimises waste by matching yarn fineness to product performance, reducing over-engineering. Brands track tex alongside lifecycle assessments to quantify material reductions and carbon savings. As bio-based fibres emerge, tex remains the lingua franca for comparing fineness and compatibility with existing machinery.

Mastering tex equips textile, composite, and additive manufacturing professionals to integrate material science with process control. Continue exploring mechanical implications through the newton article and rheological considerations within the viscosity guide.