Read the care line first
Every yarn page here carries the mill's care instruction in the spec card — "Hand wash, dry flat", "Machine wash cold, gentle" — and it is the one line on the ball band to keep. When the band is gone, the fiber decides: untreated wool, alpaca, mohair and cashmere are hand wash; superwash wool, most cotton and linen, and the merino-acrylic blends go in a machine on a cold gentle cycle. When in doubt, hand wash; nothing is ever harmed by it.
Hand washing
Fill a basin with cool water and a wool wash (a no-rinse one saves a step). Submerge the piece, press it under, and leave it for fifteen minutes; do not rub, wring or run water onto it — agitation plus heat is what felts wool, and either alone is harmless. Lift it out supporting the whole weight, press out water against the side of the basin, then roll it in a towel and stand on the roll. Lay it flat to dry, shaped to its measurements. A knit should never hang wet: wool stretches, alpaca and cotton stretch and do not come back.
Machine washing
Only for yarns whose band says so. Cold water, the gentlest cycle, a mesh bag for anything small, and the spin cycle is fine — it is the heat and the tumbling that do damage. Then flat to dry. Superwash wool can go through a cold wash for years; it will still felt in a hot one, and it stretches more than untreated wool when wet, which is why "dry flat" is on the band. A dryer is only for the few yarns that say so (HiKoo Simplicity, Plymouth Baby Alpaca Worsted, Sirdar Snuggly Cotton), on low.
Fiber by fiber
Untreated wool (Lamb's Pride, Nature Spun, Lopi, Malabrigo Worsted): hand wash, cool, no agitation; it felts if any of that is ignored, as the felting guide explains. Superwash wool (Rios, Arroyo, Edition 3): machine cold gentle, dry flat. Alpaca: hand wash, press, dry flat, and handle it wet with both hands — it is the fiber most likely to grow. Cashmere: hand wash in cool water, never hot, dry flat; it pills, and a sweater comb keeps it. Mohair and brushed suri: hand wash, do not rub, and shake it out when dry to lift the halo. Cotton and linen: machine wash cool, lay cotton flat (it stretches hung wet), tumble linen on low, which only softens it. Silk blends: hand wash cool, no wringing; silk is weak when wet. The fiber comparison is the side-by-side.
Blocking
Blocking is washing plus shaping: the wet piece is laid out to the pattern's measurements and left to dry that way. Wool holds the shape it dried in, which is why a lace shawl must be stretched and pinned — it looks like a rag until it is — and why a sweater's edges stop curling after the first wash. Pin lace hard; pat garments to size without stretching; steam cotton and acrylic blends rather than wet-blocking them, since they will not hold a pinned shape. Block before seaming, and block again after every wash by laying the piece out properly.
Pilling
Every yarn pills a little where it rubs — under the arms, at the cuffs, under a bag strap — and soft single-ply and cashmere pill most, plied and superwash least. Pills are loose fiber ends tangling, not the fabric wearing out: take them off with a sweater comb or stone, never by pulling, and they come back less each time. The single-ply vs plied guide says which yarns to expect it from.
Storing, and moths
Clothes moths eat animal fiber — wool, alpaca, cashmere, mohair, silk — and their larvae do the eating, in the dark, in anything undisturbed and preferably a little dirty. Three rules: store knits clean, since sweat and food are what attract the moth; store them folded in a drawer or a sealed bin, never hanging and never in an open basket; and air them out and refold them once a season. Cedar and lavender discourage moths while fresh and do nothing once they have faded; a sealed bag for the summer does more. If you find holes or webbing, freeze the piece in a bag for 72 hours, wash it, and check everything that shared the drawer. Yarn in the stash wants the same: a sealed bag per project.
Socks
Hand-knit socks are the one knit that must survive a machine, so they are knit in superwash wool with nylon and washed cold, gentle, inside a mesh bag, then laid flat or hung by the cuff. Hot water felts the cuff; a dryer shrinks the foot. Darn a thin heel before it goes, and the sock yarn guide is about choosing a yarn that takes longer to get there.
Pass the care on
A gift knit gets washed by someone who did not read the ball band. Tuck a note in with it: the fiber, "hand wash cool, dry flat" or "machine cold gentle, dry flat", and the yarn's name so they can ask. It is the difference between a sweater worn for years and one washed once.