The complaint arrives as a photograph: a T-shirt whose side seam has crept round to the front, or trouser legs whose inside seam spirals down the shin. The fabric was within its shrinkage limits. It simply rotated.
That rotation is what AATCC 179 measures. It is not shrinkage, and a laboratory that only runs AATCC 135 will not see it.
What the method measures
AATCC 179, Skew Change in Fabrics after Home Laundering, applies to woven and knitted fabrics suitable for home laundering, and to garments. Marks are applied to the specimen before laundering, the specimen is laundered, and the alignment of the marks is measured afterwards. The result is a percentage skew plus the direction in which it occurred.
The terms are worth keeping straight:
- Skewness — the filling yarns or knitted courses are displaced at an angle from a line perpendicular to the fabric edge.
- Garment twist (also called torque or spirality) — panels of a garment rotate relative to each other as latent stresses in the fabric are released during laundering.
AATCC 179 measures the change caused by laundering. Skew already present in the fabric as received is a separate property, covered by bow-and-skew methods such as ASTM D3882. A fabric finished off-grain can show high as-received skew and little change on washing, or the reverse.
ISO has its own route for spirality after laundering, the ISO 16322 series, which earlier AATCC 179 editions listed as related.
Trap 1: comparing reports from different editions
This is the one that causes the most confusion, because the method has changed in two visible ways.
| Older editions (e.g. 2004 text) | Current TM179-2025 (AATCC summary) | |
|---|---|---|
| Laundering before measurement | Five cycles, or an agreed number | Two standard laundering cycles |
| Sign of the result | Calculation option 1 gave positive for left, negative for right | Calculations do not give negative values; direction recorded separately |
A historical report of "−4.1 %" and a new report of "4.1 %, right" may describe the same behaviour. A new report after two cycles and an old one after five do not describe the same test. When a customer compares this season's result with a figure from an old specification, check which edition — and how many cycles — the old number came from.
Trap 2: the specimen was already distorted
AATCC 179 warns that fabrics or garments distorted in their unlaundered state — through faulty finishing or faulty garment assembly — can give deceptive results. If the courses already run at an angle before you mark, the "change" you measure is partly the fabric relaxing back from a forced position.
Before marking, lay the specimen flat and look along the courses or filling yarns. If they are visibly off-grain, record it, and consider measuring as-received skew separately so the two effects are not blended.
Trap 3: tubular knits handled the wrong way
Earlier editions of AATCC 179 made the distinction clearly: tubular knit fabric intended for tubular end use (underwear, sweatshirts, polo shirts) is tested in tubular form; tubular fabric that will be slit and cut flat is slit and handled flat. Testing a tubular body fabric as a flat slit specimen removes the very constraint that produces twist in the garment.
Trap 4: measuring a wrinkled specimen
The diagonal or perpendicular distances that AATCC 179 uses are long compared with the deviation being measured. A ridge or wrinkle across the measuring line shortens it. Condition the specimen after laundering, lay it on a flat surface without tension, and smooth only enough to remove folds. As with shrinkage, do not iron unless the method and the end use call for it.
Trap 5: mixing calculation options between laboratories
The method has offered more than one marking and calculation option — square marking with diagonal measurement for fabric specimens, and an inverted-T marking for garment panels. Earlier editions stated plainly that the options are related mathematically, but that laboratories comparing data should use the same option. Put the option on the report.
Trap 6: not recording the direction
Because the current edition does not produce negative values, the direction exists only in your records. "3.8 %" on its own does not say whether the fabric turned left or right — and any corrective action in production depends on exactly that. Have the person who measures write the direction for each specimen at the time of measurement, not reconstruct it later from a photograph.
Fabric versus garment
A fabric test predicts tendency. A garment test shows the outcome, because twist in a garment also depends on how the panels were cut and sewn. If the complaint is about finished garments, test garments — the largest panels — rather than fabric specimens alone.
Reporting checklist
- Edition of AATCC 179, and number of laundering cycles.
- Washing cycle, temperature and drying procedure (in words).
- Fabric or garment; for knits, tubular or slit.
- Marking and calculation option used.
- Percent skew and direction for each specimen, plus the average.
- Any visible distortion before laundering.
AATCC 179 is run on the same top-loading machine and tumble dryer as AATCC 135, so the two tests share laundering conditions. Our AATCC shrinkage washing machine and AATCC tumble dryer are built in our own workshop in Istanbul.