Thread thickness, often expressed as Tex size, is a fundamental specification in garment production and home sewing alike. The right thread thickness ensures seams hold under stress, fabrics behave correctly during stitching, and final garments wear well over time. Yet many quilters, hobbyists, or OEM producers stumble when trying to translate fabric weight into the correct Tex size. This guide unpacks the concept of Tex, explains how to convert between Tex and other sizing systems, and provides practical guidelines for selecting the right thread thickness for various fabrics and stitch types. By the end, you’ll be able to read thread labels with confidence, perform quick on-factory conversions, and communicate precise thread requirements to suppliers and sewing operators.
What is Tex? The core idea of thread thickness
Tex is a measurement that expresses the weight, in grams, of 1,000 meters of thread. In other words, Tex answers the question: “How much does a long length of this thread weigh?” The key relationship is inverse: as the weight per 1,000 meters increases, the Tex value decreases, indicating a thicker, heavier thread. Conversely, a higher Tex value corresponds to a thinner, lighter thread. This inverse relationship is essential when you’re translating a fabric’s needs into a concrete thread choice.
Commonly cited example: a thread rated as 40 wt (weight in the weight system used by many sewing brands) converts to about Tex 25, because Tex = 1000 / wt, so Tex = 1000 / 40 = 25. This simple formula connects two widely used sizing conventions and helps manufacturing teams align expectations with suppliers.
For reference, you’ll also encounter denier, another sizing system. Denier describes the weight in grams of 9,000 meters of thread. The relationship to Tex is roughly Denier ≈ Tex × 9. For the example above, Tex 25 corresponds to about 225 denier. Understanding these conversions gives you flexibility when sourcing thread from different regions or suppliers who adhere to different standards.
Why thread thickness matters in sewing and production
Thread thickness affects stitch quality, seam strength, and fabric behavior. The wrong thickness can lead to skipped stitches, thread breaks, puckering, or seam slippage. In a factory setting, incorrect thread thickness can trigger quality issues, returns, or brand reputation problems. The Tex size you choose should reflect fabric weight, fiber content, stitch type, and the expected stress on the seam. For example, a denim garment will usually use a much thicker, lower-Tex thread than a delicate silk blouse. Similarly, topstitching often benefits from a slightly thicker thread to create a defined line without weakening the seam.
Understanding Tex also helps when communicating with dye houses, trims suppliers, and sewing machine technicians. If a line sheet lists a “Tex 25” thread for a heavyweight canvas, a seamstress will know to expect a sturdy yet not extremely bulky stitch. If the same line calls for “Tex 60” for a lightweight chiffon, you’ll know to choose a very fine thread that won’t add bulk or cause puckering. Clear Tex sizing reduces ambiguity across design, sourcing, and production teams.
How to convert and read Tex from a label
Most thread labels show either the weight (wt) in the traditional system or the Tex value, sometimes both. To determine the Tex from a weight, use the formula:
Tex = 1000 / Weight (wt)
Examples:
- If a thread is labeled as 40 wt, Tex = 1000 / 40 = 25 Tex.
- If a thread is labeled as 60 wt, Tex = 1000 / 60 ≈ 16.7 Tex.
- If a thread shows Tex 30, the implied weight per 1,000 meters is Weight = 1000 / Tex = 1000 / 30 ≈ 33.3 grams per 1,000 meters.
To understand Denier from Tex, use Denier ≈ Tex × 9. So Tex 25 corresponds roughly to Denier 225, while Tex 16.7 corresponds to Denier about 150. When you work with international suppliers, knowing both Tex and Denier can help you compare options quickly across production lines.
Which Tex size should you choose for different fabrics?
General rules of thumb help you map fabric weight to thread thickness. These guidelines are not absolute, but they work well as a starting point in both OEM production and home sewing projects.
- Lightweight fabrics (silk chiffon, voile, fine cotton lawn): Seek higher Tex values (finer threads) for delicate fabrics to avoid adding bulk and to minimize puckering. Tex 40–60 or higher is common for topstitching and fine seams on sheer fabrics.
- Medium-weight fabrics (cotton poplin, chinos, twill): A mid-range Tex is appropriate, often Tex 25–40. This range balances strength with a comfortable hand and clean stitch formation.
- Heavy fabrics (denim, canvas, heavy velvet): Choose a lower Tex (thicker thread) to provide seam strength and durability. Tex 12–25 is typical for heavy-duty seams and topstitching on rugged textiles.
- Stretch fabrics (knits with elastane or spandex): Fiber content matters as much as thickness. A moderate Tex with good elongation may be ideal, with a focus on thread elasticity and compatible needle size.
- Specialized functions (topstitching, decorative stitches): You may deliberately select a lower Tex for a bold topstitch or a higher Tex for a delicate decorative seam, depending on the fabric and stitch type.
Remember that these ranges serve as a starting point. For a production run, you may run tests with two or three Tex options on representative fabrics and evaluate seam strength, puckering, needle heat, and thread cut performance. In many OEM contexts, you’ll develop a recommended thread chart aligned to fabric weight bands, stitch types, and performance targets.
Practical steps to specify Tex in a production BOM
In a formal Bill of Materials (BOM) for garment manufacturing, including thread thickness as a line item helps procurement and QA teams verify consistency across lots. Here are practical steps to include Tex sizing in your BOM and production workflows:
- Fabric classification: Assign a weight class to each fabric family (light, medium, heavy) and note fiber content (cotton, polyester, blends, denim, silk, etc.).
- Stitch type mapping: For each seam type (construction seam, side seam, topstitch, edge finishing, lockstitch), specify a recommended Tex range and needle size.
- Thread color and finish: Note any finish, coating, or colorfast requirements that might influence thread choice (e.g., mercerized cotton for sheen, polyester for durability).
- Supplier data: Record the Tex value supplied by each vendor, along with the Denier if provided, to facilitate cross-sourcing and reorders.
- QA checkpoints: Include a standard test protocol for seam strength, abrasion resistance, and needle heat with the specified Tex, so inspectors know what to measure on first articles and during mass production.
When you document Tex in your BOM, add a short rationale column explaining why a particular Tex range was selected for a fabric. This helps new team members and factories abroad reproduce the same results consistently, reducing variance across lots and seasons.
How to test and validate thread thickness on the sewing floor
Testing is essential when introducing new fabrics or changing suppliers. A practical test plan might look like this:
- Prepare samples: Cut multiple swatches of each fabric with the same pattern piece to ensure consistency.
- Choose tonal contrasts: Test with one or two thread colors to ensure visibility and colorfastness do not influence your assessment.
- Run stitch tests: Stitch a sample with the recommended Tex options and different seam allowances. Record stitch length, tension, and results.
- Evaluate seam integrity: Perform tensile tests or manual stress checks to assess seam strength, pucker, and thread breakage.
- Assess aesthetics: Check thread visibility, fiber shedding, and finish quality. Ensure the thread sits flat against the fabric without snagging or creating a bulky seam.
- Document results: Capture notes and photographs, label which Tex performed best for each fabric, and update the BOM with any adjustments.
Industrial suppliers and OEM facilities often maintain a thread test library. If you’re building or managing such a library, categorize by fabric family, weight class, and stitch type, and store test photos and data for quick reference during new line launches or material changes.
Common pitfalls and how to avoid them
Even experienced teams encounter pitfalls when specifying Tex. Here are the most frequent issues and practical ways to prevent them:
- Assuming higher Tex always equals weaker seams: While higher Tex indicates a finer thread, it can still provide excellent seam strength when paired with the right needle size, tension, and stitch type. Don’t assess thread thickness in isolation; consider the full stitching system.
- Ignoring fabric stretch and recovery: Knits and blends can behave very differently from wovens. If a fabric stretches during wear, a finer thread might produce a looser seam, or conversely, a thicker thread might cause distortion. Conduct specific knit tests for stretch fabrics.
- Overlooking needle compatibility: The needle size must align with the thread thickness and fabric. A mismatch can cause skipped stitches, bird-nesting, or fabric damage.
- Relying on a single “best Tex”: For a multi-fabric collection, you might standardize on a few Tex references and allocate them to fabric weight bands rather than trying to optimize every single fabric individually. This reduces complexity while maintaining quality.
- Not accounting for thread finish and coating: Some threads have coatings (e.g., waxed, bonded, or plied) that affect friction, tension, and needle wear. Factor finish into your testing and BOM decisions.
Real-world case studies: applying Tex sizing in different contexts
Case study A: A denim line. For heavy-weight denim, a robust seam is essential. A typical approach is to choose a lower Tex value, such as Tex 20–25, to deliver strong, visible seams and reduce the risk of seam failure under abrasion. In production, the team might run a test with Tex 20 and Tex 25 to observe seam behavior under washing and wear as well as shade retention and thread pilling.
Case study B: A lightweight cotton poplin shirt. Here, a higher Tex thread (Tex 35–50) is often chosen to minimize seam visibility and avoid creating a stiff seam that could affect drape. The goal is a nearly invisible, smooth seam with consistent stitch formation across the garment.
Case study C: A silk-blend evening dress. Delicate fabrics demand fine threads that do not show through the fabric or create bulk at the seam. A Tex around 40–60 is common for construction seams, with careful testing of tension to avoid puckering and breakage during finishing or steaming processes.
Materials and sources: practical tips for procurement
When sourcing thread thickness, you’ll often encounter vendors that provide multiple sizing standards. These tips help keep procurement efficient:
- Ask for a material spec sheet: Request the thread’s weight per 1,000 meters (wt), Tex, and denier. If possible, have the vendor provide both Tex and denier so you can compare with other suppliers.
- Request a test lot: Before committing to a full order, obtain a sample spool with the exact Tex rating and test it on representative fabrics. Keep notes on tension settings and stitch performance.
- Use conversions when necessary: If your supplier uses Denier, you’ll benefit from knowing Tex × 9 to compare. Conversely, if a vendor uses Tex, you can estimate weight per 1,000 meters and compare to the label’s Latin or Cyrillic equivalents if needed.
- Document packaging and labeling: Ensure packaging includes clear Tex or wt values so operators can quickly verify they’re using the correct thread across shifts.
Glossary
Tex: A unit describing the weight in grams of 1,000 meters of thread. Higher Tex means thinner thread, lower Tex means thicker thread.
Weight (wt): The weight in grams of 1,000 meters as used in the standard sewing thread labeling. Tex = 1000 / wt.
Denier: The weight in grams of 9,000 meters of thread. Denier ≈ Tex × 9.
Seam strength: The ability of a seam to withstand pulling and stress without breaking or coming apart.
Puckering: Distortion or gathering along a seam caused by incorrect tension or thread thickness relative to fabric.
Quick-reference cheat sheet
Use this quick guide to map typical fabric families to Tex ranges, keeping in mind that testing is essential for final decisions:
- Lightweight fabrics: Tex 40–60+
- Medium-weight fabrics: Tex 25–40
- Heavy fabrics: Tex 12–25
In the end, the goal is to choose a thread thickness that delivers reliable stitch performance, preserves fabric integrity, and aligns with production efficiency and cost targets. The Tex system gives you a precise, scalable language to communicate those requirements across teams and suppliers. With methodical testing, clear documentation, and cross-functional collaboration, specifying thread thickness becomes a repeatable, data-driven process that supports high-quality garment outcomes.
If you’re building a new line or optimizing an existing line, consider establishing a standard thread thickness chart tied to fabric weight bands, stitch types, and finishing processes. This reduces guesswork, speeds up sourcing, and improves consistency across seasons. For OEM partnerships, a well-documented Tex specification supports faster onboarding of new factories and ensures that your brand quality remains consistent from first cut to final inspection.
Next steps: gather your current fabric weight data, set up a small seven-piece test matrix covering a few Tex options per fabric, and compare seam strength, puckering, and hand feel. Use the results to finalize your internal thread thickness reference table and update your BOMs. A small upfront testing investment can pay dividends in reduced returns, better wear performance, and more predictable production timelines.
