What dimensional stability means
Dimensional stability is a fabric's ability to keep its size and shape through washing and drying. Change can go either way. Most complaints are about shrinkage, but some fabrics grow, especially in length, and some twist so that side seams spiral toward the front. Each of these changes the fit the customer bought.
Activewear is close-fitting, so small changes matter. A loose meditation top can absorb a little shrinkage without anyone noticing. A legging that loses length at the inseam or tightens at the waist after the first wash feels like a different size.
Why knitted activewear changes size
Knitted fabrics are stretched and held under tension during knitting, dyeing and finishing. If that tension is not fully relaxed and the fabric is not properly set, it tends to return toward a more relaxed state the first time it is washed and dried. Several factors decide how much change is left in the fabric when it reaches the cutting table.
- Heat setting at the mill: synthetic and spandex blends are heat set to stabilize their dimensions. Incomplete setting leaves residual shrinkage.
- Fiber: nylon and polyester blends are generally more stable once set; cotton, modal and viscose blends tend to move more in washing.
- Spandex share: higher spandex content means more elastic force in the fabric, which can pull the fabric smaller if it is not well set.
- Fabric handling: fabric that is cut straight from a tightly wound roll, without being allowed to relax, can shrink after sewing.
- Care conditions: hot washing and high-heat drying cause more change than the gentle care most activewear is designed for.
How AATCC 135 measures it
AATCC 135 is a common method for dimensional change of fabrics after home laundering. In general terms, benchmarks are marked on a fabric specimen, the specimen is washed and dried under specified conditions, and the distance between the marks is measured again. The result is reported as a percentage change in length and width, with shrinkage and growth both possible.
| Item | What it means | Why it matters |
|---|---|---|
| Length change | Change along the length of the fabric | Affects inseam, rise and garment length |
| Width change | Change across the fabric | Affects waist, hip and thigh |
| Wash and dry conditions | Temperature and drying method used in the test | Should match or be gentler than the care label |
| Number of cycles | How many wash and dry cycles were run | More cycles show whether change continues or settles |
Acceptance levels for dimensional change are agreed in the order specification, in both directions, together with the test conditions. A shrinkage figure without the wash and dry conditions next to it is hard to interpret.
Fabric test versus garment wash test
A fabric test tells you how the material behaves. A garment wash test tells you how the finished product behaves, including seams, waistband elastic, binding and any fused or bonded parts. Both are useful, and they answer different questions.
- Fabric approval: ask for AATCC 135 results on the finished fabric, at conditions consistent with your intended care label.
- Sample garment: measure the sample at key points, wash and dry it at care label conditions, and measure again.
- Compare with tolerance: check the after-wash measurements against the tolerances in your tech pack and size chart.
- Check twist: lay the garment flat and see whether side seams or inseams have rotated.
- Record the reference for bulk: approved fabric result plus garment measurements before and after washing.
Connecting shrinkage to the size chart
Patterns are sometimes made with an allowance for expected shrinkage. That works only if the shrinkage is consistent from lot to lot. If the fabric is well stabilized, a smaller allowance is needed and the fit is more predictable. Ask the partner factory whether the pattern includes a shrinkage allowance and which test result it was based on. The size chart and grading note explains how tolerances are set across sizes.
Write the size chart from washed-garment measurements where possible, or at least check that unwashed measurements still sit within tolerance after a wash. Customers measure the garment they own, not the garment as it left the factory.
Sets need one more check. If a top and a bottom are cut from different fabrics, or from the same fabric in different lots, they can shrink by different amounts. Wash-check both pieces together so a matching set still fits as a set after the first few washes.
The care label closes the loop
The Care Labeling Rule (16 CFR 423) requires care instructions on apparel. For activewear, those instructions should describe the conditions under which the fabric was tested and approved. If dimensional change was tested at a cool wash and low-heat drying, the label should say so. A label that allows hot water or high-heat drying invites the shrinkage the test was meant to prevent. See the US labeling rules note for the label requirements.
Fabric-specific notes
Nylon and spandex interlock, the usual legging fabric at 230-280 GSM, is generally stable once properly heat set, and the main risk is incomplete setting or a lot that was finished differently. Brushed fabrics go through an extra mechanical process that can affect stability, so test the brushed version. Organic cotton, modal and viscose blends, common in loose yoga clothes, usually need more attention to shrinkage and twist, and care instructions for them tend to be more conservative. The fabric library covers each fabric family.
On bulk and reorders
At bulk stage, ask for a dimensional change result on the bulk fabric lot before cutting, and include a garment wash check on the first finished pieces. On reorders, repeat both, since a different dye lot or finishing run can change the result. If a customer complaint mentions shrinkage, compare a retained sample from the same lot with the approved reference before deciding on the cause.
We include dimensional change in the fabric test plan coordinated with the mill and in the measurement checks of the quality control process. If your line mixes synthetic leggings with cotton or viscose pieces, send the desk your fabric list and intended care instructions so testing and labels are aligned from the first sample.