How to wash a wool sweater without shrinking or felting it

To wash a wool sweater, turn it inside out and either soak it for 10 minutes in lukewarm water with a wool detergent, or put it on your machine's wool cycle if the care label says machine wash. Then press the water out in a towel and dry it flat, away from heat and direct sun. Rubbing and tumbling in water are what shrink wool, and heat makes it worse, so every step below keeps the water mild and your hands gentle.

The rule: no hot water, no rubbing, no hanging

Each wool fiber is covered in microscopic scales. The Woolmark Company explains that heat and moisture make the scales lift, and agitation then locks them onto the scales of other fibers like a ratchet. The knit tangles, thickens and shrinks, and the change is irreversible. That's felting.

Machine-washable wool, which the industry calls superwash, has been treated so the scales can't lock. You can't see the treatment, so the care label, not the fiber, decides how your sweater gets washed. US labels use words or symbols, and under the FTC's Care Labeling Rule the maker has to give a washing or a dry-cleaning instruction, plus a warning when a step you'd reasonably expect to take would harm the garment.

The gap between Dry clean and Dry clean only is real. The same rule lets a maker list just one safe method even when a garment can be washed and dry-cleaned, and it allows "Dryclean Only" only when the maker has evidence that washing will damage the garment. A plain wool or cashmere knit labeled "Dry clean" may hand wash well, but that's your call and your risk. Leave it to the cleaner if it has leather trim, beads or colors you'd hate to see run.

How to hand wash a wool sweater

Hand washing is the gentlest option, and the right one for anything labeled hand wash. You need a clean basin or sink, a wool detergent and two towels.

1. Turn the sweater inside out.
2. Fill the basin with lukewarm water, about 86°F (30°C), as Woolmark's washing guide advises. That's cooler than a bath. Dissolve the detergent in the water before the sweater goes in.
3. Push the sweater under and let it soak for 10 minutes.
4. Squeeze the suds through it gently a few times. Don't rub, pull or wring it: Woolmark's guide to care symbols says to let the garment float in the water and move it carefully.
5. Drain the basin and rinse the sweater thoroughly in lukewarm water, then once more in cold.
6. Lift it out with both hands underneath it. Wet wool is heavy and stretches under its own weight.

Don't leave it soaking for hours or lying wet in the empty basin. The same guide says colored and delicate pieces should be washed quickly and not left sitting wet.

Cashmere takes cold water. The Cashmere and Camel Hair Manufacturers Institute says to hand wash cashmere knits in cold water with a detergent made for wool, cashmere and silk, never wring or twist them, and dry them flat on a dry towel.

How to wash a wool sweater in the washing machine

Only machine wash a sweater whose label says so. The care label has to be safe to follow, so a wool sweater labeled machine wash is one that can go through the machine without shrinking, and those are the sweaters these steps are for.

1. Turn it inside out, or zip it into a mesh laundry bag.
2. Pick the wool cycle, which Woolmark describes as gentle action, usually at 104°F (40°C). If your machine doesn't have one, use the cold wash or the delicates cycle.
3. Add a mild, neutral wool detergent. If it's a powder, dissolve it in water first.
4. Keep the drum no more than a third full, as the care-symbol guide advises for machine-washable wool.
5. Wash dark and pale sweaters separately, and don't leave them lying together wet, where the colors can bleed.
6. Take the sweater out as soon as the cycle ends and dry it flat, unless the label says tumble dry.

The detergent matters as much as the cycle. Woolmark's detergent guide says to avoid heavy-duty detergents, "bio" detergents with enzymes and anything with bleach, chlorine or oxygen. Wool is a protein fiber, and the enzymes in bio detergents are there to break down protein stains. The same guide warns that undissolved powder can leave concentrated specks that may cause holes, and that too much fabric softener helps pills form in later washes.

How to dry a wool sweater flat, and fix one that lost its shape

A wet sweater on a hanger or a clothesline stretches. Woolmark's drying guide says the weight of the water pulls a knit longer and out of shape, and a hanger can push bumps into the shoulders, wire hangers most of all. So wool knits dry flat:

1. Lay the sweater on a white or pale towel, since a colored one can bleed, and roll the two up together, pressing as you roll to squeeze the water out. Don't twist.
2. Unroll it and move the sweater to a dry, lint-free towel or a mesh drying rack. Racks made to sit over a bathtub dry it faster.
3. Pat it back to its shape and size: sleeves straight, shoulders square, hem and cuffs back to their width, creases smoothed out.
4. Leave it in the shade, away from direct sun, a sunny window, a radiator or a heat vent. Over a radiator, the part lying on the heat dries first and can change color or get damaged.
5. When the towel under it is damp through, swap in a dry one and turn the sweater over.

The dryer is out unless the label says tumble dry. Wool labeled tumble dry can go on low heat or a wool or delicates setting; anything else is best dried flat.

If it came out wrong, most of it can be fixed:

• Bumps on the shoulders from a hanger: the drying guide's fix is to dip just those areas in warm water, 86 to 104°F (30 to 40°C), and massage them gently. Let the sweater dry flat, and it normally goes back to its shape.
• Longer than before after hanging to dry: wet it, press the water out in a towel and pat it back to its old length and width as it dries flat.
• Shrunk: if the stitches have blurred into a thick, stiff fabric, it has felted and won't come back. Woolmark says recovery isn't possible when a hand-wash or dry-clean-only sweater went through a washing machine and felted badly. If it only tightened a little, wet it and ease it back toward its old size as it dries flat; you may win back some of it.

How often to wash a wool sweater, and what to do between washes

Less often than you might think. Woolmark says wool resists odors, stains and creases, so it needs less washing. There's no set number of wears: wash a sweater when it still smells after airing, when it has a stain a damp cloth won't lift, or when it's going into storage for the season.

Between wears, four habits keep a sweater fresh without water:

• Air it. Woolmark's care tips say that laying wool flat on a bed or a towel for an hour lets food and smoke odors go.
• Rest it. The same tips suggest 24 hours before you wear a wool piece again, so the fibers can spring back to their shape. Two or three sweaters worn in turn make that easy, and if you mark what you wear in gussy, its calendar shows which one has had its day off.
• Wear a layer under it. A T-shirt or a shirt keeps sweat and body oil off the wool.
• Fold it. Knits belong folded in drawers, while woven wool goes on hangers. The fold-or-hang table in how to organize your closet covers the rest of your clothes.

Wash every sweater before it goes away for the summer. Food stains and body oils attract moths, so wool should be clean before it's packed into airtight bags or boxes.

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