Fabric Shrinkage Testing: Methods, Calculation and Limits

Why shrinkage matters for Pakistani exporters

In FY2024-25 Pakistan exported US$5,010.5 million of knitwear, up 13.68%, and US$4,128.6 million of readymade garments, up 15.85%. Together that is 51.1% of US$17,887.0 million in textile exports (Towel Manufacturers' Association of Pakistan, from Pakistan Bureau of Statistics data).

Shrinkage does not show at a pre-shipment inspection. The inspector measures garments as packed; how they change in the first wash only a laundering test can show. A garment that loses a size in the customer's machine comes back as a return, after the order has been paid for and shipped.

Why fabric shrinks

Turning yarn into fabric, and finishing it, puts tension into the fabric. Washing lets the fabric relax from those tensions, and it shortens. Cotton Incorporated's guide to shrinkage performance makes three points that matter for a specification (Cotton Incorporated, ISP 1009):

• Processing forces that stretch the fabric give more shrinkage later; forces that compress it give less. Poor control of these forces in processing can lead to high garment shrinkage.

• Woven fabrics are much more stable than knitted fabrics, but much lower shrinkage limits are demanded of wovens, so processing tension matters just as much for them.

• Finishing plants reduce shrinkage with relaxation drying, compaction and chemical processes.

That is why the test belongs on the bulk lot being cut. Two lots of the same quality, finished on different days, can relax by different amounts.

The test methods: ISO and AATCC

ISO 6330 warns that the washing machine type, the detergent and the type of tumble dryer can all affect the result (ISO). Two labs running "ISO 5077" on different procedures can report different numbers for the same fabric, so name the exact procedure, not only the standard.

How a shrinkage test works

• Mark. The lab marks measured distances on the specimen, in the length (warp or wale) and width (weft or course) directions.

• Measure. The marks are measured before washing.

• Wash and dry. The specimen goes through the named washing and drying procedure, for the number of cycles in the specification.

• Re-measure and calculate. Dimensional change (%) = (distance after − distance before) ÷ distance before × 100, reported separately for length and width, with the direction: shrinkage or growth.

A garment test measures named points on the garment, such as body length, chest and sleeve, instead of marks on a square of fabric.

Worked example: a single jersey T-shirt fabric

A lab marks 50.0 cm in the length and 50.0 cm in the width of a knitted fabric specimen. After the specified washing and drying, the length marks measure 46.5 cm and the width marks 51.0 cm.

• Length: (46.5 − 50.0) ÷ 50.0 × 100 = 7.0% shrinkage.

• Width: (51.0 − 50.0) ÷ 50.0 × 100 = 2.0% growth.

• To finish a 70 cm body length, the pattern is cut at 70 ÷ 0.93 = 75.3 cm.

• To finish a 50 cm half chest, the pattern is cut at 50 ÷ 1.02 = 49.0 cm.

If the buyer's limit were, say, 5% length shrinkage, this fabric fails, and the right fix is at the mill: relaxation or compaction before cutting, not a bigger pattern. The figures are worked for illustration, not taken from a real test. The denim quality control guide works the same calculation for jeans.

Spirality, skew and bow

Some fabrics do not just shrink, they twist. A side seam that walks to the front of a T-shirt, or a jeans leg that turns, cannot be corrected once the garment is sewn.

ISO notes that results from different spirality procedures will not always be comparable, that some constructions such as denim can have spirality introduced on purpose, and that fabrics from circular knitting machines can have an inherent lean in the wales (ISO 16322-2). Agree the procedure and the limit before the fabric is bought.

Fabric test or garment test

Running both catches different faults. A fabric that passes can still give a garment that fails, for example when a fused part and the body fabric shrink by different amounts.

Write the requirement into the order

• The method: ISO 5077 with ISO 6330 and ISO 3759, or AATCC TM135 or TM150

• The washing procedure and temperature, and the drying procedure, matching the care label

• The number of wash and dry cycles

• Whether the test is on fabric, garments or both, and at which stage

• The limit for length and for width, each with its direction, for example shrinkage no more than 5% and growth no more than 2%

• The spirality or skew method and its limit, for knits and twills

The lab testing guide covers how to plan the rest of the test programme for an export order.

Tti Labs shrinkage and dimensional stability tests

These methods are on the Tti Labs ISO/IEC 17025 scope, PNAC LAB-022, valid until 8 Aug 2027:

Each test and its charge are confirmed in writing, with the turnaround, before any work starts (Tti Labs testing).

Ask Tti Labs for a shrinkage test