What Does Pre-Shrunk Mean?

How is fabric pre-shrunk?

Fabric is pre-shrunk by letting it shrink in the mill, before it is made into a garment, so that it will not shrink much later in the wash. The aim is to release the tension that weaving, knitting and finishing build into the cloth.

Compressive shrinkage

Compressive shrinkage, also called relaxation shrinkage, is applied to cotton and cotton blends. Britannica describes it as typically spraying the fabric with water and pressing it against a heated cylinder covered with a felt or rubber blanket. The treatment increases the density of the warp and weft yarns.

Relaxation drying and compaction

For cotton knits, Cotton Incorporated groups two steps as “consolidation shrinkage”. In relaxation drying, the fabric shrinks as the wet fibres and yarns deswell. Compaction uses compressive forces, from heated roll-and-shoe compactors or compressive belt systems, to shorten the fabric and reduce its length shrinkage.

Sanforized is a narrower case: Merriam-Webster records it as a collective mark used for fabrics preshrunk by a mechanical process.

Why does fabric shrink in the first place?

Most cotton shrinkage is stored tension coming out: yarn and fabric are stretched in production, then pull back when they are wetted and tumbled. Cotton Incorporated lists tension from knitting, take-down, spreaders and machine transport, and notes that continuous dyeing and preparation processes usually stretch the fabric in length and reduce its width.

• Stretching in wet processing. Extraction is the single greatest concern for length distortion in knit fabrics; length stretch of 10 per cent and higher is commonplace.
• Swelling and drying. Water swells the fibres and yarns. The greatest relaxation occurs at moisture levels below 20 per cent; the bulletin calls the level at which fibres deswell “critical moisture”.
• Knits versus wovens. Woven fabrics are much more stable than knitted fabrics, so a jersey T-shirt is more exposed than a woven shirt.

Wool shrinks a second way

Wool can also shrink by felting. The Woolmark Company explains that untreated wool fibres carry microscopic scales, which lock onto each other when the fibre is agitated in water. It calls the process irreversible. Machine-washable wool is treated to modify those scales so they cannot interlock.

How is shrinkage measured?

Shrinkage is measured by washing and drying a fabric sample under set conditions and reporting the change in length and width as two percentages. Cotton Incorporated uses AATCC Test Method 135, which washes and tumble-dries the fabric without tension, and recommends at least five cycles for complete, reliable results.

Results are written length × width, for example “5.0 × 5.0%”. Its figures for one 100 per cent cotton interlock show what each processing step does:

Extraction pushed length shrinkage up to 20.0 per cent, and the + sign means the width grew rather than shrank in the wash test. Compaction then cut length shrinkage from 9.0 to 5.0 per cent, while width shrinkage was 8.0 per cent against 7.0. One headline number can hide the other direction. There is no universal target either: the bulletin says specifications are agreed between the customer and the mill.

What does “pre-shrunk” mean on a clothing label?

On a label, “pre-shrunk” tells you the maker has reduced shrinkage, not removed it. Britannica notes that manufacturers often specify the residual shrinkage percentage left after compressive shrinkage.

In the US, the Federal Trade Commission’s business guide to the Care Labeling Rule does not mention the word “pre-shrunk”. What it does require is a reasonable basis for all care instructions and warnings, and that instructions, if followed, cause no substantial harm to the product.

The FTC has acted where garments shrank. In 1997 it announced that a New Jersey importer had agreed to pay a $4,000 civil penalty, under a proposed consent judgment, over alleged care-label errors on rayon blouses, skirts and dresses. The FTC said the clothes shrank significantly when hand-washed as instructed; the settlement was not an admission of a violation.

How do you tell whether a pre-shrunk garment will keep its size?

You tell by the figure behind the claim and by your own first wash, not by the word itself. These checks need only the label and a tape measure.

1. Ask for the number. A maker who has tested will have a length × width figure and a method, such as AATCC 135 over five cycles. A bare “pre-shrunk” with no figure tells you less.
2. Read the drying line. For cotton, Cotton Incorporated notes that if the label calls for line or flat drying, mostly elastic shrinkage will affect the garment. If it suggests tumble drying, all available residual shrinkage will be realised.
3. Check knit or woven. Look at the cloth: interlocking loops mean a knit, which the bulletin says is much less stable than a woven.
4. Measure before the first wash. Lay the garment flat and note body length and chest width. Wash and dry it as the label says, then measure again. For cotton, Cotton Incorporated says one wash-and-dry cycle may remove around 90 per cent of the shrinkage available, so the first wash should show most of the change.
5. For wool, look for a machine-washable claim. Felting is a separate risk from relaxation shrinkage, and it is the scale treatment that addresses it.

Red flag: a seller who calls a garment pre-shrunk but cannot say by how much, or by which test.

How do you care for pre-shrunk clothes?

Follow the care label, and treat the tumble dryer as the main risk to size. In a Cotton Incorporated test, a cotton interlock tumble-dried at 38°C, 66°C and 94°C (100°F, 150°F and 200°F) gave identical shrinkage curves, so in that test the drying temperature made no difference.

Pre-shrinking controls size only. Whether the colour will run is a separate question of how colourfast the dye is; the same applies to garment-dyed pieces.