More sweaters are ruined by the washing machine than by moths. A shrunk hem, a stretched neckline, a surface gone dull and pilled — nearly all of it happens on wash day, not while the sweater is being worn. How to wash a wool sweater without ruining it comes down to a short list of rules, most of which take no longer to follow than the wrong method you were using before.
Can You Machine Wash a Wool Sweater?
Some can, most shouldn't risk it. A superwash or treated wool, and most acrylic and acrylic-blend knits like the Alpine Crewneck, can generally go through a machine on a wool or delicate cycle, cold water, inside out, in a mesh bag, and at the lowest spin setting the machine offers. Untreated 100% wool is a different case: the agitation and heat of a standard machine cycle is exactly what causes felting, the process where wool fibres lock together and the garment shrinks and toughens for good — a felted sweater cannot be unfelted, no matter how carefully you treat it afterward. When the care label is unclear, faded or missing altogether, treat the sweater as untreated wool and hand wash it — the ten extra minutes cost far less than a ruined sweater, and the habit is worth keeping even once you learn a piece can technically take the machine.
Hand-Washing Knitwear, Step by Step
Fill a basin with cold or lukewarm water — never hot — and a small amount of a wool-safe or delicate detergent. Submerge the sweater and press the water through it gently; never rub, twist or wring, since that is what stretches and felts the fibres. Let it soak for five to ten minutes, then rinse in water of the same temperature until the water runs clear. A sudden change in water temperature between washing and rinsing is another common cause of shrinkage, so keep both steps at the same temperature throughout.
Why Knit Shrinks — and How to Stop It
Shrinkage in wool is caused by three things acting together: heat, agitation and a sudden temperature change. Remove any one of the three and the risk drops sharply — which is why cold water and gentle handling do most of the protective work. Acrylic and acrylic-blend knits shrink less easily than wool but are more prone to losing shape if hung wet, since the fibre stretches under its own water weight rather than shrinking. Either way, the fix is the same: keep the water cool, keep your hands gentle, and never wring.
Drying Without Losing the Shape
This is the step that decides whether a sweater still fits the same after its first wash. Never hang a wet knit — gravity pulls the shoulders and neckline out of shape within hours, and a stretched knit does not return to its original size on its own. Instead, lay the sweater flat on a clean towel, gently ease it back into its original shape and dimensions — a light version of what's known as blocking — roll the towel to press out excess water, then lay it flat again on a dry towel or drying rack away from direct heat or sun. Reshaping this way every time you wash it is what keeps a knit looking new for years rather than one season.
How Often Should You Actually Wash It
Less often than you likely think. Wool has a natural resistance to odour that synthetic fibres don't share, and washing more than necessary is one of the fastest ways to wear out a knit's shape and surface — every wash cycle, however gentle, is still wear on the fibre. Air a sweater out overnight on a hanger away from direct heat after wearing it and it will often need no wash at all; reserve a full wash for visible marks, or after several wears in a row where a clean airing is no longer enough. The Willow Zip Knit and the Vesper Sweater are both built from medium-weight knits that hold their shape well between washes, which makes this the easiest rule in the list to actually follow — and the one that adds the most seasons to a knit's working life for the least effort.
Get the washing right and a good knit will outlast several washing-machine-damaged ones bought to replace it — see our note on buying mistakes to avoid on the jacket you'll layer it under for the other half of the equation. Explore the full men's knitwear edit or the women's knitwear edit, or find more fabric and care questions answered on Style Answers.