One Wash, and the Hoodies Were a Size Smaller
A Guide to Fabric Shrinkage and Colorfastness Testing - Why Clothes Shrink and Bleed After Washing, How Cotton Knits, Wovens, Denim, Polyester and Spandex Blends Compare, Shrinkage (ISO 6330, AATCC 135) and Wash, Rubbing, Perspiration and Light Fastness (ISO 105) Test Criteria, Pre-Shrinking, Soaping and Dye Fixing Spec Items, Checks at Fabric, Sample and Production, Request Wording, Real Cases and a Checklist

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An online apparel brand had a factory in China produce 2,000 hoodies in 100% cotton. The samples fit well and felt soft, so mass production was approved right away, and the pre-shipment inspection found measurements within tolerance. Two weeks into sales, though, reviews started coming in: "It shrank a full size after one wash," and "I washed it with a white T-shirt and now the T-shirt is light blue." Return requests passed 300 within a month.

Tracing the cause led back to the fabric. To hit the deadline, the fabric mill had skipped pre-shrinking (预缩) and cut the soaping (皂洗) step that washes out unfixed dye after dyeing down to a single pass. The purchase order said only "全棉卫衣布 380g" (cotton hoodie fabric, 380g). Nowhere did it say how much shrinkage after washing was acceptable or what color fastness grade was required.

Shrinkage and color bleeding don't show on a new garment. They appear only after the customer's first wash, which is why routine inspection rarely catches them. This article covers why clothes shrink and bleed, what shrinkage and colorfastness tests labs run, how to set the criteria, and what to put in your spec and inspection plan.

Shrinkage and bleeding are decided in the customer's first wash. Lock the fabric finishing steps down in writing, and set post-wash shrinkage (%) and colorfastness grades as numbers.

1. Why Clothes Shrink and Bleed

Shrinkage and bleeding happen when tension and dye left in the fabric during manufacturing are released in the wash. The same fabric can behave very differently depending on how it was finished. These are the causes we see most often.

• Relaxation shrinkage (松弛收缩): Fibers stretched during knitting, weaving and finishing return to their natural length once wet. This is especially large in knit fabrics.
• Skipped pre-shrinking or heat setting: Cotton is stabilized by mechanical pre-shrinking (预缩), and polyester or spandex blends by heat setting (定型). Both cost time and money, so they get dropped when the spec doesn't require them.
• Overstretching on the stenter: If fabric is pulled wide on the stenter frame to hit the width, it shrinks back after washing. If width shrinkage is unusually large, suspect this.
• Unfixed dye (浮色): Cotton dyed with reactive dyes keeps loose dye on the fiber unless it is soaped thoroughly, and that dye comes out in large amounts in the first wash.
• Fixing agents and dye grade: The darker the color, the more fixing agent (固色剂) treatment and dye quality matter. Cheaper dyes can give the same shade with lower fastness.

For a factory, pre-shrinking and soaping are the easiest places to save cost and time. It is not unusual for samples to go through the full process while production fabric quietly skips steps. You can't see the difference by looking, so tie the finishing steps and test criteria to your documents.

2. Shrinkage and Bleeding by Fabric Type

Each fiber and construction shrinks and bleeds differently. You need to know what your fabric is before you can set test conditions and criteria.

We covered importing textiles and apparel in general in Episode 67, and managing color differences between lots in Episode 45. This article focuses on what changes after washing.

3. Shrinkage and Colorfastness Tests at the Lab

You can't borrow your customers' washing machines, so labs test fabric and finished garments with set temperatures and wash and dry methods. Knowing the test names is enough to ask a factory "Which standard, what temperature, and what were the results in percent and grades?"

How to Read the Results

Colorfastness is rated 1 to 5 on the grey scale (灰卡), where 5 means no change at all. Light fastness alone uses the blue wool scale from 1 to 8, so don't compare its numbers with the other fastness grades. If the report lists "color change (变色)" and "staining (沾色)" separately, check staining on its own, because that is the grade that tells you whether white clothes will get dyed.

For shrinkage, minus (-) means the fabric got shorter and plus (+) means it grew. When you get results, also check the wash temperature and drying method (tumble dry or line/flat dry). If the care label says "wash at 30°C, tumble dry OK" but the test used only flat drying, the result is far from real-world use.

4. Spec Items That Prevent Shrinkage and Bleeding

"全棉卫衣布 380g" alone doesn't tell a factory which fabric to use or how to finish it. Write everything down as numbers, from the fabric to the test conditions.

For writing spec sheets in general, see Episode 59. Agreeing in advance whether tests are done in the mill's own lab or at an outside lab such as SGS, Intertek or CTI also cuts down on disputes over results.

5. How to Check at Each Stage

Fabric Stage

Most garment factories don't make their own fabric; they buy it from mills. So when fabric arrives, check shrinkage and colorfastness before cutting. Get a test report for each fabric lot, and confirm with photos that the lot number on the report matches the labels on the rolls that actually came in.

Sample Stage

When samples arrive, keep one as is and wash another three times at home following the care label. Measure body length, chest width and sleeve length before washing, and throw in a white towel to check for staining. It costs nothing and tells you a lot. For dark products, rubbing the outer surface ten times with a damp white cloth gives a rough idea of wet rubbing fastness.

First Article and Production Stage

Run a wash test on the first garments made from production fabric and compare them with the sample results. Agreeing on finishing conditions and test criteria at the pre-production meeting makes this much easier. We covered that in Episode 123. At pre-shipment inspection, have the inspector wash a few finished garments on site, measure the change, and match the fabric lot numbers against the test reports. For pre-shipment inspection, see Episode 100.

6. Sample Request Wording for the Factory

Putting the wording below in your purchase order or spec makes it harder for the factory to cut finishing steps, and leaves a basis for assigning responsibility if shrinkage or bleeding occurs.

"本产品面料须完成预缩和定型处理，染色后须充分皂洗并进行固色处理。按ISO 6330（40℃洗涤，平摊晾干）洗涤3次后，面料长度和宽度尺寸变化率须在±5%以内，成衣主要部位尺寸变化不超过±1.5cm。色牢度要求：耐皂洗变色4级、沾色3-4级以上；耐摩擦干摩4级、湿摩3级以上；耐汗渍、耐水3-4级以上。每批面料须提供第三方检测报告，报告批号须与实际入库布卷一致。深色与浅色拼接的款式须做沾色测试。如需更换面料厂、纱线、染料、固色剂或调整加工工序，须事先取得我方书面确认。"
(The fabric for this product must be pre-shrunk and heat set, and must be thoroughly soaped and treated with a fixing agent after dyeing. After 3 washes per ISO 6330 (40°C wash, flat dry), fabric length and width change must be within ±5%, and key garment measurements must not change by more than ±1.5cm. Colorfastness: washing color change grade 4 and staining 3-4 or better; rubbing dry grade 4 and wet grade 3 or better; perspiration and water 3-4 or better. Provide a third-party test report for each fabric lot, and the lot number on the report must match the rolls actually received. Styles combining dark and light colors require a staining test. Any change of fabric mill, yarn, dye or fixing agent, or any adjustment to the finishing process, requires our written approval in advance.)

7. Three Real Cases

These are anonymized versions of patterns we often see in consultations. Amounts and figures are examples.

Case 1 — Brushed Cotton Hoodies

This is the case from the opening. Leftover stock and samples went through the same wash test: after 3 washes, the sample shrank 3.2% in length and the production units 7.8%. Wash staining was grade 4 on the sample and 2-3 on production. From the next run, the spec listed pre-shrinking, the number of soaping passes, and shrinkage and fastness limits, and a test report was required for every fabric lot. Fabric went up about 2 yuan per meter, which was small next to the cost of return and exchange shipping.

Case 2 — Navy and White Color-Blocked Knit

The fabric passed its own wash fastness test, yet claims came in that the white panels turned light blue after the first wash. Only the fabric had been tested on its own. Nobody had checked staining on the finished garment, where dark and white pieces are sewn together. The claims dropped only after color-blocked styles were wash-tested as finished garments and the navy fabric got a stronger fixing treatment.

Case 3 — Raw Denim Jacket

A month after launch, reviews piled up: "It left blue on my white sofa," and "The strap area of my bag turned blue." Checking showed wet rubbing fastness at grade 1-2. With indigo, raw denim can't be made fully rub-proof. So a fixing treatment was added to bring it up to grade 2-3, and the product page and care label got the line "Wash separately the first few times; avoid rubbing against light-colored materials." Once the criteria were set as numbers and customers were warned up front, returns for the same issue dropped noticeably.

8. Common Mistakes

• Defining fabric only by fiber and weight, like "全棉 380g"
• Assuming production fabric will match because the sample was fine
• Testing only the fabric, not the finished garment with color blocking and trims
• Test wash conditions that don't match the care label
• Cutting to finished measurements without building shrink allowance into the pattern
• Looking only at color change and missing the staining grade

9. Shrinkage and Colorfastness Checklist

Spec and Contract Stage

• Fiber content, construction, weight and width are in the spec
• Pre-shrinking, heat setting, soaping and fixing steps are stated
• Wash conditions and the shrinkage tolerance are set
• Grades for washing, rubbing, perspiration, water and light fastness are set
• An approval clause covers changes of mill, yarn, dye or finishing

Fabric and Sample Stage

• Matched each fabric lot's test report against the roll labels
• Washed samples three times per the care label and checked measurements and staining
• Checked staining on color-blocked styles as finished garments
• Both sides keep a set of approved samples

Production and Shipment Stage

• Compared first article wash results with the sample results
• Measured finished garments after washing at pre-shipment inspection

Wrapping Up - Start by Putting One Sample in the Washing Machine

Of all quality problems, shrinkage and bleeding are the ones customers notice fastest and most surely. A garment that shrank after one wash doesn't get worn again, and sometimes a claim for the stained white clothes follows. Count the returns, exchanges and falling star ratings, and keeping pre-shrinking and soaping in place is not a big cost.

There's something you can do right now. If you have stock or samples, take one, measure it, and wash it three times with a white towel following the care label. If the length shrank more than 5% or color came off on the towel, rework your fabric finishing and test criteria before the next order.

StartMade supports you on the ground in China: writing fabric specs, checking test reports for each fabric lot and lab results, wash-testing first articles, and verifying on site before shipment. If you already have shrinkage or bleeding claims, we start with root cause analysis; if you're preparing a new product, we start with the fabric standard.