Fabric Shrinkage: Why It Happens and How to Control It

Shrinkage is a change in the length or width of a fabric or garment. Cotton Incorporated, in ISP 1009, defines that change as able to go in a positive direction (growth) or a negative one (shrinkage). In a later CottonWorks webcast, Overcoming Shrinkage, the same organisation adds a mill definition: shrinkage or growth is the difference in dimensions between the delivered state of a fabric or garment and its reference state, the fully relaxed condition in which it will not change further as a result of washing and tumble drying.

Knitted fabrics of all constructions and fibre blends are inherently more prone to shrinkage than wovens, Cotton Incorporated states in TRI 3011, and a cotton knit is easily distorted in processing.

Yarn count, stitch length and machine gauge set the tightness of a weft knit and therefore much of its construction shrinkage; see Yarn Count Systems Explained. Fabric mass is GSM, which will itself change if the cloth shrinks. Single jersey is particularly liable to skew as well as to length change; see Single Jersey vs Rib vs Interlock. Laboratory fabric tests more generally are covered in Fabric Testing: Methods, Equipment and What Results Mean.

Diagram of four shrinkage mechanisms: elastic or relaxation shrinkage, swelling and drying shrinkage, consolidation by relaxation drying or compaction, and felting of wool.
Self-made diagram for this article. The three cotton mechanisms follow Cotton Incorporated, ISP 1009. Felting follows The Woolmark Company, Machine Washable Wool.

Why fabrics shrink

For cotton, ISP 1009 divides shrinkage into construction shrinkage and processing shrinkage. Construction shrinkage comes from the yarn and the way the fabric was made, and it can be measured on greige cloth before later processes. Processing shrinkage is what dyeing, finishing and apparel manufacture add to or remove from that construction shrinkage, and so change the residual shrinkage. Residual shrinkage is what remains after a process has stretched or compressed the cloth.

Several mechanisms sit inside those two headings.

Elastic, or relaxation, shrinkage is a change in dimensions as the fabric freely relaxes from tensions experienced during construction and later processing. On a cotton greige knit, ISP 1009 cites tensions in forming the knitted loop and from the take-down and spreader, and also stresses in bleaching, dyeing and finishing.

Swelling and drying shrinkage need more energy. When a cotton fabric wets out without tension, the fibres and then the yarns swell. ISP 1009 explains that the crimp in the yarn loops increases, and the loops try to assume a more round, lower-energy shape. That rounding shortens the loop and the fabric changes dimension. In drying, the structure deswells and shrinks upon itself. Bound water acts as a lubricant, and mechanical action then produces still more shrinkage. The greatest relaxation occurs at moisture levels below 20 per cent, a point ISP 1009 calls critical moisture; drying shrinkage normally needs more energy than elastic shrinkage. It may take several wet-and-dry cycles to reach fully relaxed dimensions, although one cycle may remove around 90 per cent of the total shrinkage available.

Consolidation is the name ISP 1009 gives to processes that force or allow the structure to contract. Relaxation drying and compaction are the two examples. Relaxation drying occurs by deswelling under unrestricted agitation with no length or width tension. Compaction is a dry mechanical effect gained by forcing the structure to compact upon itself.

Felting is a wool mechanism, not a cotton one. The Woolmark Company explains that untreated wool fibres have microscopic scales on their surface. When the fibres are exposed to heat and moisture the scales lift, and with mechanical agitation they lock onto the scales of other fibres in a ratchet-like way.

Cotton Incorporated’s webcast makes a further point that is easy to miss: the actual shrinkage of the yarns is very small and is not significant to fabric shrinkage, except for fibres that are sensitive to heat. The conversion of yarns into fabric creates stress, and that stress creates openness in the structure, tightness factor in knits or cover factor in wovens, which later relaxation can close up.

Knits and wovens, cotton, wool and synthetics

Woven fabrics are much more stable than knitted fabrics and do not react as severely to stresses, ISP 1009 states, but the shrinkage specifications demanded of wovens are often much lower, so processing stresses still matter. In a knit, TRI 3011 says the amount of shrinkage depends mainly on the product specifications and the knitting parameters used to meet them: the sold weight, stitch counts and width, and then the yarn count, gauge, number of needles and stitch length. For a given yarn count, knitting a smaller loop results in a heavier, more stable fabric, with less length shrinkage but higher width shrinkage for any specified finished width.

Cotton is not stabilised by heat. The CottonWorks webcast puts it plainly: heat does not shrink cotton fabrics. Excess heat may cause yellowing, a stiffer hand or slower re-wetting, but not shrinkage. The question-and-answer paper adds that cotton cannot be set at a temperature in the way polyester can. Polyester, nylon and elastane are heat-settable, and fibres such as spandex can shrink with heat, but in a cotton–spandex blend heat setting is only effective on the spandex; there is normally not enough spandex to stabilise the fabric against shrinkage, although heat and time can drastically affect stretch and growth. High heat on cotton blends can also reduce absorbency and give a drier hand.

Wool can felt as well as relax. Machine-washable treatments, which Woolmark describes under the industry term Superwash, improve shrink resistance by removing or smoothing scales, reducing inter-fibre friction, or both. The widely commercialised Hercosett route is a chlorine pre-treatment followed by a polyamide-epichlorohydrin resin that bonds to the fibre surface. Superwash is a category; Hercosett is one technology within it.

How shrinkage is tested

A laboratory dimensional-change test has three parts: the specimen is prepared, marked and measured; it is washed and dried under a specified procedure; and the change is then determined.

ISO 3759:2011, confirmed in 2022 and also adopted as EVS-EN ISO 3759:2011, specifies the preparation, marking and measuring of textile fabrics, garments and fabric assemblies for tests of dimensional change after a specified treatment, for example washing, dry cleaning, soaking or steaming, following procedures in ISO 3005, ISO 7771, ISO 6330, ISO 3175 or ISO 15797. The official abstract states that it applies to woven and knitted fabrics and made-up textile articles, but not to certain upholstery coverings.

ISO 6330:2021, also EVS-EN ISO 6330:2021, specifies domestic washing and drying procedures for textile testing, including reference detergents and ballasts. The official abstract provides for 16 washing procedures on a Type A horizontal-axis, front-loading reference machine, 12 on a Type B vertical-axis, top-loading agitator machine, and 7 on a Type C vertical-axis, top-loading pulsator machine. Each washing procedure represents a single domestic wash. Six drying procedures are specified: line dry, line drip dry, flat dry, flat drip dry, flat press, and tumble dry. A complete test consists of a washing and a drying procedure, and different machine, detergent or dryer parameters can affect results.

ISO 5077:2007, confirmed in 2022 and adopted as EVS-EN ISO 5077:2008, specifies a method for determining the dimensional change of fabrics, garments or other textile articles after an appropriate combination of those washing and drying procedures. The EVS catalogue page adds a caution from the standard’s scope: in the case of textile articles or deformable materials, it is necessary to exercise all possible caution in the interpretation of the results. That caution matters for knits. The official catalogue pages do not publish the calculation clause of ISO 5077, so no rounding rule from that clause is quoted here.

In North American work the usual fabric method is AATCC TM135-2025, Dimensional Changes of Fabrics after Home Laundering. The official store abstract states that it determines length and width changes of fabrics after home laundering, with four washing temperatures, three agitation cycles and four drying procedures, and that it applies to all fabrics suitable for home laundering. AATCC TM150-2025 is the companion method for garments; its abstract uses the same wash and dry options, and notes that it may not apply to garments made of certain stretch fabrics. ISP 1009 describes the principle of AATCC TM135 as a tensionless wash followed by tumble drying that deswells and fully relaxes the fabric or garment.

Diagram of a dimensional-change test: ISO 3759 for marking and measuring, ISO 6330 for washing and drying, and ISO 5077 for determining the change, with a worked length and width percentage example.
Self-made diagram for this article. The roles of ISO 3759, ISO 6330, ISO 5077, AATCC TM135 and TM150 are taken from the official catalogue abstracts. The worked percentages are arithmetic illustrations of the Cotton Incorporated definition (a percentage of the initial dimensions), not a measured fabric.

How to calculate the percentage

Cotton Incorporated’s webcast states that, in the testing laboratory, dimensional change is expressed as a percentage of the initial dimensions of the specimen. The change can be a growth, an increase of the length or width, or a shrinkage, a decrease of those dimensions. Some products shrink in one direction and grow in the other.

The CottonWorks Q&A is explicit that shrinkage numbers are for one direction only. Each direction must be measured and listed separately. The numbers are not added to each other, and they are not averaged. The example given there is that 5 × 5 per cent means 5 per cent in the length and 5 per cent in the width.

A worked arithmetic illustration, using that definition, is as follows. A marked length of 250 mm is measured again after the specified wash and dry and is 240 mm. The change is a decrease of 10 mm, or 4 per cent of the initial 250 mm, reported as a 4 per cent shrinkage. A marked width that increased from 250 mm to 255 mm would be a 2 per cent growth. The two results are reported separately. AATCC sells a shrinkage scale that reads percent change directly, but the official TM135 and TM150 abstracts do not themselves print a formula.

How far one wash cycle takes you towards the reference state depends on the product and the method. ISP 1009 states that one cycle may remove around 90 per cent of the total shrinkage available, and that several cycles may be needed for fully relaxed dimensions. The webcast describes five home-laundry tumble dries as a practical route to the reference state, with three such cycles accounting for 95 per cent of the shrinkage.

How to control it

TRI 3011 lists four influences on dimensional stability: knitting parameters, processing tensions after knitting, relaxation techniques in finishing, and mechanical and chemical finishes. The CottonWorks webcast similarly asks for specifications of weight, cut-and-sew width and allowable shrinkage, and says that drying under the lowest tensions with maximum mechanical action, together with compaction and resin finishing, will reduce shrinkage.

Start in knitting. TRI 3011 and the shrinkage webcast handout both put stitch length and tightness at the centre of consistent shrinkage: maintain stitch length, knit a tightness factor as high as is practical, keep spreader and take-down tensions consistent, and choose a machine diameter that gives a good cut-and-sew width with low and balanced shrinkage.

Keep processing tensions down. TRI 3011 stresses overfeed, driven rolls and slack-loop control in inspection, extraction, slitting and tentering. The Q&A notes that wet, especially light, fabrics will stretch in length before they can turn undriven rollers.

Relaxation drying is described in TRI 3011 as one of the most significant advances towards shrinkage reduction for the finisher. A relaxation or belt dryer places wet fabric onto an open mesh belt in a relaxed form and dries it with forced hot air and tensionless mechanical action, for both open-width and tubular knits. Because there is no width restriction, width usually shrinks first, so some width adjustment, tensionless entry and controlled overfeed are needed afterwards.

Compacting compresses the course loops upon themselves. TRI 3011 describes two broad classes of machine: heated rolls and shoe units, or belt shrinking units. Both rely on a speed differential and a compaction zone; tubular and open-width systems are available. The fabric is steamed and then compacted, with heat and moisture helping to shorten the length stitches. Softener and moisture have a large effect on efficiency, and corrugation can come from over-compaction, uneven softener or the wrong moisture. CottonWorks records the resulting compactor creases when wrinkles on a folded tubular selvage are compressed into hard creases. The Q&A cautions that compaction generally will not remove much more than 50 per cent of the shrinkage present before the process, so it should not be the only means of control.

Sanforizing is, in that same Q&A, a trade name for compressive shrinkage, now often used to cover compaction in general. It is a physical process that forces the fabric to shrink upon itself; if it is done properly, the surface will not be changed. TRI 3011 notes that a Sanforize unit, normally used for wovens, can also be used as a compactor for knits. An endless elastic belt is stretched over rollers, the fabric is introduced between the belt and a usually steam-heated drum, and the belt is then allowed to shrink, compressing the fabric. The Q&A is clear about a limit: Sanforizing does not improve filling shrinkage on any fibre content.

Heat setting has to be stated carefully. As already noted, heat does not set cotton or shrink cotton fabric. For polyester, nylon and elastane the Q&A treats heat setting as a real process, but in a cotton–spandex blend it is only effective on the spandex and will not, by itself, stabilise the cotton structure. Times and temperatures are not given on the official pages used here, so none are quoted.

Anti-felting treatments are the wool route already described: Superwash-type shrink-resist treatments, including Hercosett, modify the scale surface so that wet agitation does not produce irreversible felting.

Chemical crosslinking, or resin finishing, is widely used on cotton, especially on open-width knits. TRI 3011 explains that crosslinking occurs through reactions of polyfunctional reactants with hydroxyl groups of adjacent cellulose chains. Benefits include wrinkle recovery, smoothness after laundering and dimensional stability; disadvantages include lower burst strength for knits, reduced abrasion resistance, possible shade change, reduced moisture regain, potential odours and sewing problems. Crosslinking can give low shrinkage without the increased bulk that compaction produces; see Easy-Care and Durable-Press Resins. Combinations of relaxation drying, compaction and crosslinking are, in ISP 1009, the way to get the most consistent residual shrinkage from lot to lot.

Diagram of six shrinkage-control steps: knitting, low processing tension, relaxation drying, compacting or Sanforizing, crosslinking heat setting and anti-felting, and cutting and sewing.
Self-made diagram for this article, after Cotton Incorporated TRI 3011 and ISP 1009, the CottonWorks Overcoming Shrinkage question-and-answer paper, and The Woolmark Company on anti-felting treatments.

Garment sizing and allowable shrinkage

There is no single standard shrinkage allowance for all cotton products. The CottonWorks Q&A says it is impossible to give a standard for all the sundry types of cotton products; what can be specified are the weight, cut-and-sew width and allowable shrinkage.

ISP 1009 notes that apparel processes often increase length shrinkage. The Q&A describes how spreading on a cutting table normally produces some gain in length and loss of width. Place as little linear tension as possible during spreading, and allow the stacked layers to relax for at least 8 hours, with 12 hours preferred, which also allows moisture regain for sewing. If fabric shrinkage is within tolerance but garment shrinkage is not, and the garment was sewn from the same tested lot, the Q&A points to stretching in cut-and-sew, or to markers that were not properly oversized.

The photograph below shows a historic pin tenter, a reminder that width has always been held during finishing. Modern open-width work still has to control width and overfeed; if tenter pins travel too far in from the selvage they can leave pin holes.

A historic pin tenter frame holding a piece of fabric by pins along its edges.
A historic pin tenter frame at Helmshore Mills, holding fabric by pins along the edges. Width has long been set this way during drying and finishing; pin holes become a defect when the pins venture too far in from the selvage. Photograph by Clem Rutter, Wikimedia Commons, CC BY 3.0. Cropped and resized to 800 pixels wide.

FAQ

Is shrinkage the same as dimensional change? Dimensional change is the broader term. It is a percentage of the initial dimensions, and it may be shrinkage or growth in length or in width. Report the two directions separately.

Why do knits usually shrink more than wovens? Knitted fabrics are inherently more prone to shrinkage than wovens, and a cotton knit is easily distorted by processing tensions, according to TRI 3011 and ISP 1009. Wovens are more stable, but they are often held to tighter shrinkage specifications.

Does tumble-dryer heat shrink cotton? Not according to Cotton Incorporated. The webcast states that heat does not shrink cotton fabrics, and that the tumble dryer shrinks cotton by stress-free mechanical action as the cloth dries. Excess heat may yellow cotton or stiffen the hand. Some synthetic fibres, including spandex, are sensitive to heat and can shrink.

Which standard should I cite on a test report? Name the preparation and measurement method, the wash and dry procedure, and the method used to determine the change. In the ISO system that is typically ISO 3759, a nominated procedure from ISO 6330, and ISO 5077. In the AATCC system, TM135 is for fabrics and TM150 is for garments.

Can compacting or Sanforizing alone meet a very tight residual-shrinkage target? Not always. The CottonWorks Q&A states that compaction generally will not remove much more than 50 per cent of the shrinkage present before the process, and that Sanforizing does not improve filling shrinkage on any fibre content.

Should I wash fabric before cutting? The Q&A says that relaxed washing and tumble drying is not practical for piece goods in a mill, because of cost and labour. In a plant, the equivalent steps are relaxation drying, compaction, a rest after spreading, and markers that allow for residual shrinkage.

Sources

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