A shrinkage limit is only comparable when the measurement and treatment conditions are comparable. “Within 5% after washing” leaves open the direction, whether growth is allowed, the wash and drying procedure, the number of cycles and the state of the material being tested.
Write those choices into the fabric order and test request before samples go to a laboratory. Then connect the fabric result to the finished garment’s fit requirements. A fabric can meet its agreed limit while a particular garment still becomes too short after care.
Specify dimensional change, including growth
Use separate requirements for the length and width directions. Knits can shorten in one direction and grow in the other, so a single shrinkage number can hide the behavior that matters to the garment.
Identify the directions on the specimen and use signed results consistently. In the calculation below, a negative result means shrinkage and a positive result means growth:
Dimensional change (%) = (measurement after treatment − measurement before treatment) ÷ measurement before treatment × 100.
For a hypothetical marked distance of 50.0 cm that becomes 48.5 cm, the result is (48.5 − 50.0) ÷ 50.0 × 100 = −3.0%. A width distance changing from 40.0 cm to 40.8 cm gives +2.0%. These are arithmetic examples, not acceptance limits or Knitwear Base test results.
Keep the raw distances with the percentages. “3% shrinkage” without a direction or sign convention is harder to reconcile than a complete measurement record.
Choose a method appropriate to the test object
ISO 5077 addresses determination of dimensional change after washing and drying. ISO 6330 provides domestic washing and drying procedures used in textile testing. AATCC TM135 addresses dimensional changes of fabrics after home laundering. Specify the selected method and edition, then have the laboratory confirm the applicable procedure and reporting requirements.
Do not present a fabric method as automatically covering a finished garment. If the approval needs garment measurements, ask the laboratory to identify an appropriate garment method and measurement plan separately. Sewing, panels, trims and garment finishing can affect the outcome.
Standards contain detailed requirements that should be taken from the applicable licensed method. This guide is a purchasing checklist, not a reproduction of a standard or a substitute for laboratory instructions. Avoid mixing parts of different methods into an unnamed test and then reporting compliance with one of them.
Complete the test specification before choosing a limit
| Specification field | What the buyer and laboratory should agree |
|---|---|
| Material identity | Fabric reference, composition, construction, color and lot |
| Test object and state | Fabric or garment; finished, relaxed or other defined condition |
| Method | Method identifier, edition and any explicitly agreed departure |
| Sampling | Lots and rolls represented, specimen quantity and sampling locations under the selected method |
| Preparation | Specimen preparation, marking and initial conditioning requirements |
| Washing | Named procedure, machine/program details and other method options required to reproduce it |
| Drying | Selected drying procedure and relevant settings |
| Cycles | Number of complete treatments and the points at which results are recorded |
| Measurement condition | Conditioning or resting after treatment and measurement procedure |
| Directions and limits | Separate signed lower and upper bounds for each required direction |
| Reporting and disposition | Raw values, individual results, summary rule, failures and responsible decision-maker |
Do not fill the open method choices with a laboratory’s unstated default. Ask the lab and supplier to acknowledge the same completed request. Where more than one lab is involved, circulate one controlled version.
Relate the program to the care instructions
Choose wash and dry conditions that address the intended product use and care instructions. Document additional conditions if the product brief requires them. A result from a gentle procedure should not be used as evidence for an unrestricted claim about every washing or drying practice.
Name the cycle count and reporting points. A result after one treatment cannot be silently compared with a result after several. If both early and repeated-care results matter, request both and define which requirements apply at each stage.
Confirm the condition in which the initial fabric was supplied. Greige fabric, finished fabric and a relaxed finished sample represent different stages. Record any pretreatment rather than allowing one supplier’s result to include an undisclosed step that the comparison sample did not receive.
Set limits from the product requirement
There is no single acceptance percentage suitable for every knit fabric and garment. Use development results, the intended fit, construction and feasible process control to agree the limits. The supplier and technical team should understand what the customer is expected to receive after care.
Write a lower and upper bound where both shrinkage and growth matter. The following uses placeholders deliberately:
Length direction: from [signed lower bound]% to [signed upper bound]%; width direction: from [signed lower bound]% to [signed upper bound]%, after [number] cycles using [method, edition and selected wash/dry procedure].
State whether acceptance is based on individual results, an agreed average or another rule allowed by the chosen method and commercial specification. An average can conceal an outlying specimen, so do not leave the acceptance rule unstated. Ask the lab to identify relevant measurement uncertainty and rounding practices when results are near a boundary.
Retain the approved fabric and its report, but do not let a physical swatch replace written limits. A swatch establishes identity and appearance; the report and specification establish the measured conditions and criteria.
Keep related tests distinct
Fabric weight is mass per unit area, not dimensional change. A fabric can change area after washing without the GSM alone explaining the full behavior. Use the GSM tolerance guide to define weight measurement separately and the same-fabric comparison guide when supplier quotations use the same nominal GSM.
Skew, spirality and seam twisting also need their own agreed assessment where relevant. AATCC TM179 concerns skew change after home laundering, but selecting that reference does not by itself define every finished-garment twist requirement. Ask the lab to confirm the test object, method and reporting needed for the actual concern.
If the garment gets shorter and wider, see the directional change troubleshooting guide. Keep a root-cause investigation separate from the acceptance calculation: a correctly calculated failure does not alone identify which finishing or pattern change will resolve it.
Reconcile results before changing production
When two reports disagree, first compare sample identity, lot, specimen state, method edition, selected wash/dry options, cycle count, conditioning and measurement records. Check the sign convention and whether one report gives an average while the other lists individual values.
Where retesting is needed, agree a representative sampling plan and comparable retained material. Record the retest purpose and how results will be used. Do not repeatedly test different specimens until one happens to pass or replace the original report without explanation.
For a failed lot, identify the affected stock and agree its disposition before use. Any proposed reprocessing, pattern adjustment or change of use needs a review of the resulting garment and specification. Passing a revised fabric test does not automatically approve the finished product.
Send a testable specification
Send the fabric reference, destination product, proposed care instructions, completed test fields and development results through Knitwear Base’s contact page. Ask the team to confirm the proposed test arrangement and flag missing conditions before the laboratory runs the assessment.
