How do you wash knitwear so it does not stretch?

A sweater two centimetres shorter in the sleeves after one wash, or a size wider across the shoulders. Knitwear reacts to washing differently than woven fabric, because it is built from loops that can shift. Everything else follows from that single fact.

Why does knitwear behave differently than woven fabric?

Woven fabric has a rigid grid of interlaced threads, while knitwear is built from connected loops that can change position under water and weight, which is why it stretches and shrinks more easily. That is structure, not the quality of the material.

The consequence is twofold. Wet knitwear weighs far more than dry knitwear and lengthens under its own weight, especially at loaded points: at the shoulders on a hanger and along the bottom edge. At the same time, too high a temperature makes the fibres shrink and the sweater gets smaller. Both processes happen in one wash, only in different parts of the garment. That is why a sweater can narrow across the body and lengthen in the sleeves at once, which looks like a contradiction and is a normal consequence of how knitting behaves.

At which temperature should you wash knitwear?

Knitwear goes up to thirty degrees, and the crucial part is that the washing and rinsing temperature stay the same, because a sudden change is what causes felting. The number itself matters less than keeping it constant.

The first two rows cover most of a wardrobe. With knitwear that has any wool in the blend, always choose the wool cycle, even when the share of wool is small.

Wool behaves in a recognisable way here. In daylight a wet weave looks darker and denser than a dry one, and in movement damp knitwear lengthens under its own weight, which is why you never lift it by one sleeve.

How do you dry a sweater without losing its shape?

Drying flat is the only method that leaves the measurements unchanged, because it removes the pull of weight on the loops. A hanger under wet knitwear lengthens the shoulders irreversibly.

• Press, do not wring. Roll the sweater in a towel and press to take the water out without twisting the fibres.
• Lay it out flat. On a dry towel, shaping it with your hands before it starts to dry.
• Away from radiators and sun. Fast drying stiffens the fibre and takes away its spring.
• Turn it halfway. After a few hours move the sweater onto a dry towel, because the underside dries more slowly and can hold a damp smell.

The order matters. Shaping after drying changes nothing, because the loops set in the position they dried in.

How do you rescue a stretched or shrunken sweater?

Both problems can be partly reversed: stretching responds to warmer water, shrinking to soaking with hair conditioner. Neither method restores the full cut, but both can recover a few centimetres, which at the sleeves is often enough.

• Stretched. Wash it in water ten degrees warmer than usual and dry flat, easing the material gently towards the middle.
• Shrunken. Soak for twenty minutes in lukewarm water with a spoonful of conditioner, then stretch it flat and pin the edges.
• Pilled. A fabric shaver along the direction of the knit, never across it. On heavier gauges this needs doing once a season at most.

What should you avoid when washing knitwear?

Four habits ruin sweaters faster than everything else put together.

• Never dry knitwear on a hanger. The shoulders push out into distinctive points that no amount of pressing will remove.
• Avoid a tumble dryer. Shrinkage in wool reaches several percent and cannot be undone.
• Never rub a stain while it is wet. Friction mats the fibres into felt that cannot be separated again.
• Avoid fabric softener on wool. It settles on the scales of the fibre and takes away its ability to manage moisture.

Frequency is a separate question. Wool does not need washing after every wear, because it does not hold smells. Airing overnight is enough, and a full wash can wait for a real stain. That rule has limits: pieces worn directly against the skin, such as fine roll necks under matching sets or soft loungewear, need washing more often, because they absorb perspiration despite a woollen blend.

Frequently asked questions

How often should you wash a wool sweater?

Every five to eight wears, far less often than cotton. Between wears, airing in a ventilated place is enough.

Can knitwear go in the washing machine?

It can, on a wool or delicate cycle, with the spin at up to six hundred revolutions. The condition is a mesh laundry bag, which limits friction against the drum.

How should you store sweaters out of season?

Folded, in a sealed box, washed and completely dry. More on protecting them from pests is in the guide to clothes moths.

Does a cardigan wash differently than a sweater?

The same way, but fasten the buttons before washing so the button band does not stretch. On cardigans that band is the most common place for the knit to lose its shape.

Go back to that sweater two centimetres shorter. Almost every time it comes down to the same moment: drying on a hanger, or water that was too hot. Both can be eliminated without buying anything, and with fine knits, thin tops worn underneath and wool hats and scarves the difference shows after the first season.