How to Wash a Knitted Jumper
Every knit fibre has a different damage mechanism. Wool felts from scale cuticle interlocking. Alpaca is more resistant but still a protein fibre. Angora loses its halo from machine agitation — not heat. Cotton knit permanently stretches under gravity when hung wet. The unifying rule: lay all knit jumpers flat to dry, never on a hanger.
The Chemistry
Knitted jumpers span a wider range of fibre types than almost any other garment category, and each fibre type has a distinct damage mechanism. The unifying principle is that knit structure — whether stocking stitch, cable, rib, or openwork — depends on interlocked loops under specific tension. Any process that changes those loops' size or tension changes the garment's dimensions. Wool jumpers felt from heat and mechanical agitation via scale cuticle interlocking: the saw-toothed scales on wool fibres ratchet in one direction and interlock irreversibly when agitation moves fibres under heat and moisture. This is permanent — the jumper has become a smaller, denser object. The solution is cold water and minimal agitation. Merino under 18.5 microns felts faster than coarser wool because finer scales interlock more efficiently with each other. Superwash merino has scales that have been either removed by chlorine gas treatment or polymer-coated, making them machine-washable. Alpaca fibre (from Vicugna pacos — the South American camelid) has a fundamentally different scale structure from wool. Alpaca scales are flatter, less pronounced, and more widely spaced along the fibre than wool scales. This means alpaca is significantly more felting-resistant than equivalent-diameter wool — it can tolerate gentle machine washing that would felt an equivalent wool jumper. However, alpaca is still a protein fibre: the fibre is damaged by alkaline conditions (high pH detergent hydrolyses the peptide bonds in the protein chain), by enzyme detergent (proteases digest alpaca fibre), and by high heat. The absence of felting risk does not mean the absence of other chemical damage risks. Angora is rabbit fibre (from Angora rabbits, not the Angora goat — that produces mohair). Angora fibres are extremely fine (12–16 microns, finer than the finest merino) and are unusual in being very long relative to their diameter — creating the characteristic fluffy halo effect. The damage mechanism for angora is mechanically distinct: the long protruding halo fibres are not attached to the yarn core by felting but by being caught in the twist of the yarn. Machine agitation physically shears these long surface fibres from their attachment points, producing pilling (which immediately sheds) and a flatter surface without the halo effect. Angora jumpers must be hand washed and must not be brushed vigorously or subjected to any abrasion. The shedding of angora fibres (the characteristic angora problem) is partly natural and partly accelerated by machine washing. Cotton knit jumpers have no felting risk (cotton has no scales) but a gravity problem. Cotton yarn has low elasticity — unlike wool or elastane-blended yarn, cotton does not spring back to its original length after being stretched. When a cotton knit garment is wet, the loops absorb water and become significantly heavier. If the jumper is hung wet, gravity pulls the loops downward, stretching them. The stretched loops dry in their new elongated shape, permanently lengthening the garment, especially at the shoulders and cuffs. Cotton knit jumpers must always be laid flat to dry — never hung on a hanger. The same gravity-stretch mechanism applies to bamboo viscose knitwear, which has even lower wet strength. Acrylic knit jumpers behave as thermoplastic polymers: the polyacrylonitrile fibre has a glass transition temperature of approximately 85–100°C. Below this temperature, the fibre maintains its spun crimp and texture. Above this temperature (in a hot tumble dryer or during a very hot iron), the surface of the fibre softens and can flow, permanently destroying the crimp texture and creating a shiny, glazy surface. Acrylic rib on cuffs and hems is particularly vulnerable because the elasticity of the rib relies on fibre crimp — if glazed, the rib loses its recovery and becomes permanently stretched. Mixed-fibre knitwear (wool/acrylic, alpaca/silk, cotton/wool blends) must be treated to the requirements of the most delicate fibre in the blend.
Step-by-step
- 1
Identify fibre content from the care label — the most delicate fibre determines the method
Read the fibre composition, not just the care symbols. 100% wool: cold hand wash, no agitation. 100% alpaca: cold hand wash or very gentle machine cold. Angora content: hand wash only, no agitation. Cotton knit: cold gentle machine wash, but always lay flat to dry. Acrylic: 30°C gentle machine wash, no high heat dry. Mixed blends (e.g. 70% wool / 30% acrylic): treat as the most delicate component — wool rules apply. When in doubt: cold hand wash is safe for all knit fibres.
- 2
Turn inside-out and use a mesh bag for machine-washable jumpers
Turning inside-out reduces pilling from abrasion against the drum and against other garments. A mesh laundry bag provides an additional physical barrier that reduces machine agitation — even on a delicates cycle, being inside a mesh bag significantly reduces the mechanical stress on knit loops. For angora content garments, a mesh bag is not sufficient — hand wash only. For wool jumpers: even with a wool wash cycle, a mesh bag is recommended.
- 3
Wash at the correct temperature for the fibre — and use the correct detergent
Wool, alpaca, cashmere, angora: cold water (20–25°C), wool-specific or enzyme-free detergent. Never biological detergent for any protein fibre. Cotton knit: 30°C gentle cycle, biological detergent is fine. Acrylic knit: 30°C gentle cycle, standard detergent. Mixed wool/acrylic: cold, enzyme-free detergent. No fabric softener on wool or alpaca — fabric softener can impair the natural scales (in the case of non-superwash wool) and can interfere with the wool's natural moisture-management properties.
- 4
Never wring — support the full weight when lifting a wet jumper
A wet heavy knit jumper can weigh 500g–1.5kg depending on size and fibre. Lifting it from one corner stretches the wet knit loops under the weight of the garment — this is a major cause of shoulder stretching and dimension change. Support the full weight with both hands from underneath, lifting the whole garment as a flat mass. Do not wring or twist. Gently squeeze water out by pressing between your hands, then transfer to a clean dry towel.
- 5
Lay flat to dry — on a dry towel, reshaped to original dimensions
This applies to ALL knit jumpers without exception. Place on a clean dry towel, smooth into the original shape, and leave to dry completely. Measure against the original measurements if precision matters. The first towel will absorb significant moisture — transfer to a second dry towel after 2–3 hours for faster drying. For chunky knits: the core of thick yarn bundles may still be damp when the surface feels dry — allow 24+ hours and check the thickest areas before storing. Never hang a wet knit jumper on a hanger — gravity stretches the shoulder seams and armhole area permanently in all fibre types.
- 6
Store folded, not hanging — gravity stretches knitwear in storage too
Fold knit jumpers rather than hanging them in a wardrobe. Even when dry, hanging knitwear on a standard hanger causes the shoulder area to stretch over time as the weight of the garment acts on the loops at the hanger contact points. Fold in thirds horizontally (not in half at the shoulder, which creates a crease at the fold line) and stack in a drawer or on a shelf. For moth prevention (relevant for wool, cashmere, and alpaca): cedar wood and lavender repel moths but do not kill eggs — the only reliable moth egg treatment is 72 hours at −18°C (home freezer).
Knit jumper washing guide by fibre
| Fibre | Method | Temp | Detergent | Dry | Damage risk |
|---|---|---|---|---|---|
| Wool (standard) | Cold hand wash or wool machine cycle in mesh bag | Cold (20–25°C) | Enzyme-free, wool-specific | Flat on towel | HIGH — scale interlocking irreversible |
| Merino wool | Cold hand wash; superwash merino: gentle machine cold | Cold (20–25°C) | Enzyme-free | Flat on towel | HIGH (standard) / LOW (superwash treated) |
| Alpaca | Cold hand wash or very gentle machine cold | Cold (20–25°C) | Enzyme-free (still protein fibre) | Flat on towel | LOW (fewer/flatter scales than wool) |
| Angora | Cold hand wash only — no machine, no agitation | Cold (20–25°C) | Enzyme-free, gentle | Flat on towel | LOW felting; HIGH halo loss from agitation |
| Cotton knit | Machine gentle 30°C | 30°C | Standard or enzyme | Flat — gravity-stretches badly when hung wet | No felting; gravity stretch if hung wet |
| Acrylic knit | Machine gentle 30°C | 30°C | Standard | Flat; no high heat tumble | No felting; glazes above Tg ~85–100°C |
Frequently asked questions
Can you machine wash a knitted jumper?
It depends on the fibre. Superwash merino and alpaca can be gently machine washed cold in a mesh bag on a wool or delicates cycle. Acrylic and cotton knit can be machine washed on a 30°C gentle cycle. Standard wool, cashmere, and angora should be hand washed cold only. Mixed blends must be treated to the requirements of the most delicate fibre in the blend. Regardless of fibre, always lay flat to dry — never hang a wet knit jumper on a hanger.
Why has my knitted jumper gone out of shape after washing?
The most common cause is drying on a hanger rather than flat. All knit fibre types — wool, cotton, acrylic, alpaca — stretch under gravity when wet because the knit loops are displaced by the weight of the wet garment. Cotton knit is particularly prone to this because cotton has low elastic recovery. The solution is always to dry knitted jumpers flat on a clean towel, smoothed back to their original dimensions, and never to hang them on a hanger while wet.
Is alpaca wool machine washable?
Alpaca is more felting-resistant than sheep wool because its scale structure is flatter and less pronounced — so it can tolerate more gentle machine washing than standard wool. A very gentle cold machine wash in a mesh bag is generally acceptable for plain knit alpaca. However, alpaca is still a protein fibre and should never be washed with biological (enzyme) detergent, alkaline detergent, or in hot water. Cold water, enzyme-free detergent, mesh bag, lay flat to dry. Alpaca blended with wool should be treated as standard wool.
How do you prevent a knitted jumper from shrinking?
For wool: always use cold water (never warm or hot) and minimal agitation — felting from scale interlocking is the primary irreversible shrinkage mechanism in wool, triggered by heat plus agitation plus moisture. Use a wool-specific or enzyme-free detergent at cold temperature. For cotton knit: avoid the dryer — heat causes residual fibre tension release in cotton, producing shrinkage. Always air dry cotton knit. For acrylic: no high heat drying. In all cases, laying flat to dry rather than hanging or tumble drying is the most effective shrinkage prevention step.