Preface
To improve the colorfastness of woven stretch fabrics, the key is to address the poor dyeability of spandex fibers and the volatilization of dyes during the high-temperature setting process required for elastic fabrics. Meticulous control throughout the dyeing and finishing stages is essential.
Because stretch fabrics contain spandex—which has a much lower dye uptake than the main fibers (such as nylon or polyester)—this is the primary cause of “white exposed” spandex after washing and poor staining fastness.
Drawing on industry experience and technical data, the following five production stages are what we control at the mill to reach high colorfastness. If you buy fabric rather than produce it, the second half of this guide is written for you: which test standards to ask for, what a passing grade looks like, and the failures that are specific to spandex core-spun constructions.
1. Weaving Stage: Ensure Proper “Covering”
This is the most fundamental step. Use nylon or polyester drawn textured yarn (DTY) to fully cover the spandex (currently, there are also filament FDY products twisted to cover spandex, but these filament stretch fabrics hold a smaller market share). The same covering logic applies to the nylon four-way stretch fabrics we weave for outdoor and workwear programs.
- Function: To completely wrap the spandex yarn, preventing it from being exposed on the yarn surface.
- Effect: During dyeing, the dye only contacts the easily dyeable nylon or polyester. This prevents the spandex—which has poor dyeability—from being directly exposed, which would otherwise lead to exposed white spandex on the fabric surface and poor colorfastness of the spandex when washed or abraded. (Note: Dyeable spandex fiber products are now available, though at a slightly higher cost than ordinary spandex.)
2. Pre-treatment: Achieve Thorough “Cleaning”
Before dyeing, it is essential to thoroughly remove residual oils, lubricants, and sizing agents from the fiber spinning and weaving processes. These impurities hinder dye adsorption and are a common cause of uneven dyeing (color spots/flowers) and reduced colorfastness.
- Recommended Process: Use a cold pad batch (CPB) process combined with open-width desizing. This is more energy-efficient than conventional scouring in a dyeing machine and causes less damage to the fabric surface (conventional machine scouring can lead to chafing and crease marks).
- CPB Formulation Reference: Caustic soda, along with a de-oiling agent and a scouring agent. Pile at room temperature for 24-48 hours, then wash thoroughly and prepare for pre-setting.
3. Dyeing Stage: Achieve Precise “Coloration”
- Nylon Stretch Fabrics (Most Common): Use acid dyes for low-temperature dyeing. The dyeing temperature should be 100-110°C. These dyes offer a wide color range and bright shades, with high affinity for nylon—they are the foundation for ensuring colorfastness.
- Polyester Stretch Fabrics: Use a high-temperature, high-pressure dyeing process with disperse dyes. The dyeing temperature should generally be 120-130°C.
- Process Control: Strictly control the heating rate during dyeing (too rapid heating can cause uneven dye dissolution, leading to dye spots/flowers). Also control the holding time (insufficient holding time can cause “crow’s feet” crease marks on the fabric surface).
4. Post-treatment: Achieve Thorough “Washing and Protection”
This is a critical step for improving fastness. It involves a three-step process: strong washing + preventing back-staining + effective dye fixing.
- Thorough Soaping: After dyeing polyester stretch fabrics, a high-temperature soaping process is necessary to remove unfixed “surface dye” from the fiber surface. A small amount of sodium hydrosulfite can also be used for reduction cleaning. Disperse dyes themselves are not completely water-soluble; sodium hydrosulfite reduces them to water-soluble “leuco forms,” thereby improving colorfastness.
- Acid Dye Fixing: During the holding phase, use an acid dye-fixing agent to form a protective film on the fiber surface, sealing the dye. This significantly improves various fastness properties, including washing and perspiration fastness.
5. Setting Stage: Avoid “High-Temperature Damage”
Excessively high setting temperatures can harden the spandex, cause it to lose its elasticity, or even melt it, thereby destroying the fiber structure and affecting the stability of the fixed dye.
- Nylon/Spandex: Conventional literature suggests setting temperatures of 185-190°C.
- Polyester/Spandex: Conventional literature suggests setting temperatures of 190-195°C.
However, these conventional temperatures mentioned in most references have already been superseded by our production practice. The above two conventional methods only yield average or poor colorfastness for spandex elastic fabrics.
We have now improved the process with the following scheme, which provides more stable dimensional stability (heat setting shrinkage) and better colorfastness.
- Nylon/Spandex: Pre-setting at 210-220°C; Final setting at 150-160°C.
- Polyester/Spandex: Pre-setting at 200-210°C; Final setting at 140-150°C.
- Setting Speed: Should be determined on-site based on the number of oven chambers and the specific airflow/air volume of the stenter frame being used.
How Buyers Verify Colorfastness Before Ordering
Everything above is what the mill controls. From the buying side, “colorfastness” is not a single number—it is a family of tests, and a supplier can be strong on one and weak on another. When you request a lab report for a stretch fabric, these are the six properties that actually decide whether the fabric will survive the wash-care label you intend to print on it.
| Property | What it measures | Common standards | Typical requirement |
| Colorfastness to laundering | Shade change after repeated home washing, plus staining of adjacent fabric | AATCC 61 / ISO 105-C06 | Change ≥ 4, Staining ≥ 3–4 |
| Colorfastness to rubbing (crocking) | Dye transfer under dry and wet rubbing | AATCC 8 / ISO 105-X12 | Dry ≥ 4, Wet ≥ 3 |
| Colorfastness to perspiration | Shade change and staining in acidic / alkaline sweat | AATCC 15 / ISO 105-E04 | Change ≥ 4, Staining ≥ 3–4 |
| Colorfastness to chlorinated pool water | Resistance to the chlorine in swimming-pool water | AATCC 162 | Change ≥ 4 (swimwear, performance) |
| Colorfastness to water | Bleeding when the fabric is soaked | AATCC 107 / ISO 105-E01 | Change ≥ 4 |
| Colorfastness to light | Fading under light exposure | AATCC 16 / ISO 105-B02 | ≥ 4 (higher for outdoor use) |
How to read the grades. AATCC and ISO report fastness on a 1–5 gray scale, where 5 is no change and 1 is severe change. Light fastness is sometimes reported on the 1–8 blue-wool scale instead, so always confirm which scale a report is using. A grade of 4 is the usual commercial floor; for a stretch fabric, a staining grade below 3 is a red flag, because it means the dye is already leaving the fiber before the garment has been worn.
- Ask for both numbers. Shade change and staining are reported separately. A fabric can hold its own color (change 4–5) while still staining a white pocket lining (staining 2), and it is the staining number that generates customer complaints.
- Test the finished fabric, not the greige or the yarn. Colorfastness is set by dyeing and finishing, so a report on raw yarn says little about the fabric you will cut.
- Insist on an accredited third-party report (SGS, Intertek, Bureau Veritas, TÜV and similar), with the report number and test date, rather than a supplier’s own statement. Reports are usually valid for a stated period—check that the date still covers your production window.
- Match the test to the end use. Swimwear and performance programs should always include AATCC 162; workwear and outdoor programs should look harder at light and rubbing fastness. Generic “4+ colorfastness” claims without the standard named are not verifiable.
Why Spandex Core-Spun Fabrics Fail Differently
Stretch fabrics do not fail the same way as rigid fabrics. Because the core yarn is a different polymer from the sheath, and because the fabric passes through high-temperature setting, there are four failure modes that buyers should be aware of—three of them are production-controlled, and one is a chemistry limit you cannot process your way out of.
1. Spandex grin-through (“white exposed”)
Spandex takes up dye far more slowly than the nylon or polyester around it, so any place where the core shows through the sheath will read as a lighter, whiter streak. It appears after the fabric is stretched or washed—exactly when the sheath opens up at the surface. The fix is upstream: tighter covering at weaving and a dyeing recipe that does not rely on the spandex to carry color.
2. Thermal migration of disperse dyes during setting
In polyester/spandex fabrics, disperse dyes can migrate back toward the fiber surface during the high-temperature setting step. The shade looks correct on the roll, then shifts or stains a lighter adjacent fabric after the garment is pressed or laundered. This is why the final setting temperature and the reduction-cleaning step matter more on polyester stretch than on nylon stretch. It is also why ordering polyester four-way stretch calls for a fabric that has been fully reduction-cleaned, not just dyed.
Coating and bonding are the two process steps that can create this failure on their own, because heat is applied again after dyeing. We have documented a case where it did: spliced 420T pongee panels that stained at the seams only after coating, and the change that brought them back into specification.
3. Spandex embrittlement at excessive setting temperature
Push the setting temperature too high and the spandex loses elasticity, hardens, or degrades outright. The dye may still look right, but the fabric has lost its stretch recovery, and the degraded core no longer holds the fixed dye as stably through washing. The low final-setting temperatures in section 5 exist precisely to avoid this trade-off between dimensional stability and fastness.
Setting is not the only place this happens. The dyebath can damage the elastane core before the fabric ever reaches the stenter — a dye system with the wrong pH, or a heating curve that climbs too fast, softens and attacks the spandex while the colour is being developed. We have seen it surface as melting and bubbling on a 160D nylon climbing fabric, traced to the dye system and pH rather than to setting; the case and the process change that fixed it are documented here.
4. Chlorine attack in pool water
Spandex is chemically vulnerable to chlorine, so chlorine-resistant performance is a limit of the fiber itself rather than something a finish can fully solve. If a program involves frequent pool or chlorinated-water exposure, the more durable route is a construction with no spandex at all—spandex-free mechanical stretch fabric (T400 / T800) gets its stretch from the yarn’s own crimp, so there is no elastane core to be attacked. Where spandex is required, specify AATCC 162 and select a chlorine-resistant elastane grade.
If you are weighing the two routes, the practical difference is covered in our guide to spandex-free stretch fabric.
We have also rebuilt a programme after this failure had already happened in the market: 4,500 swim trunks faded after three seasons on an elastane blend, and the fix was a change in yarn composition rather than in the dyeing recipe.
Final Summary
Is your stretch fabric made of nylon, polyester, or another fiber? The dye and fixing agent systems vary significantly depending on the fiber, and the fastness standard you need depends on the end use. Please provide the specific composition and the wash-care label you plan to print, and we will recommend the dyeing, fixing and setting route that meets it. You can also put those requirements into our guide to writing an RFQ for woven stretch fabric and we will quote against it.
