Merino vs Lambswool vs Cashmere: What the Wool Labels Actually Mean

Three words dominate wool knitwear labels, and none of them means what shoppers usually assume. “Merino” describes a breed, “lambswool” describes an age at shearing, and “cashmere” describes a different animal entirely — so the same rack can hold fibers that behave very differently on the body. The reliable way to compare them is not the breed name but two measurable specs: fiber diameter, measured in microns, and staple length, the length of the raw fiber. Diameter governs what skin reads as softness. Staple length governs how the yarn ages. Together they predict pilling, price and even how a sweater should be washed.

Microns decide whether wool itches

Fiber diameter is measured in microns — a micron is one millionth of a meter — and it is the single biggest driver of what skin reads as softness. Fine fibers bend on contact; coarse fibers poke. As New Mexico State University’s wool grading guide sets out, coarse fibers above 30 microns feel stiff and suit carpets and heavy outerwear rather than next-to-skin knits. Merino spans roughly 15 to 24 microns, with ultrafine grades under 17.5 and superfine between 17.5 and 19.5, per wool industry grading summaries. Cashmere runs finer still — typically 14 to 19 microns, with premium grades between 14 and 16.5. Lambswool is the wildcard: because the term refers to a sheep’s first shearing at around seven months rather than a breed, its diameter varies widely, often averaging around 25 microns. Its softness comes from a different mechanism — each fiber still carries its naturally tapered, unshorn tip, which is gentler than the blunt cut end of re-shorn adult wool.

Staple length explains pilling and price

Diameter is only half the spec sheet. Knitwear analysis published by Wide Open World puts cashmere staple at roughly 28 to 42 millimeters against 50 to 140 for merino, and the consequence is mechanical: fibers are twisted into yarn like strands into rope, so short fibers work loose and pill under friction while long fibers stay anchored. That is why cashmere pills more readily and loses shape faster, and why long-staple merino holds a crisp surface through years of wear. Price follows scarcity and verification rather than brand myth. Urban Caps’ wool industry overview notes that ultrafine merino represents under 5% of global production, and that certification and testing regimes — Woolmark, OEKO-TEX, the Responsible Wool Standard — add laboratory costs ordinary wool never carries. Merino also yields less clean fiber per kilogram of greasy fleece, so mills need more raw material for the same garment.

Warmth and moisture behave differently too

Merino’s crimped structure traps air and lets the fiber absorb up to 30% of its weight in moisture without feeling wet, releasing it gradually — which is why performance brands build base layers from it. Cashmere wins on warmth-to-weight: its loft traps more insulating air per gram, which is why a thin cashmere sweater rivals a chunky lambswool one. Lambswool sits in between — warm and springy, with a lofty hand that comes from its short staple, but less elastic memory than merino and less refinement against the skin.

Care requirements split along the same lines

The care differences follow the fiber specs. Cashmere’s short, fine fibers make it the most fragile of the three: hand washing in cool water is the standard guidance, and knitwear should be dried flat, since hanging stretches a wet sweater’s shoulders — a point commercial cleaners’ symbol guides make for all wool knits. Merino is more forgiving, especially in superwash-treated form, which tolerates a gentle machine cycle. Lambswool handles machine washing on wool cycles better than cashmere but still prefers flat drying. All three are protein fibers, so moth-proofing storage matters more than any single wash decision.

Label	Fiber source	Typical diameter	Staple	Care bias
Merino	Merino sheep fleece	15-24 µm	50-140 mm	Gentle machine or hand wash, dry flat
Lambswool	Any breed, first shearing	~22-28 µm	Short	Wool cycle, dry flat
Cashmere	Goat undercoat	14-19 µm	28-42 mm	Hand wash, dry flat, moth-proof storage

What the label is allowed to tell you

Few brands print a micron count, which is why the rest of the label does so much work. A blend percentage is the first check: “30% merino” means the other 70 percent is something else, usually a cheaper wool or a synthetic, and the hand of the fabric follows the majority fiber. The word superwash on a tag signals a machine-washable treatment, with the trade-offs described above. Third-party marks carry verifiable information: Woolmark, OEKO-TEX and the Responsible Wool Standard all involve laboratory testing that ordinary wool never goes through, so their presence is one of the few quality signals in the category that can be checked rather than felt. When a brand does print a micron figure — ultrafine and superfine grades are the ones most likely to — treat it as the strongest claim on the label, because it is the one number that can be measured against the ranges above.

How a wool sweater actually gets ruined

Three failure modes account for most dead wool knits, and each traces back to a fiber spec. The first is felting: heat and agitation swell and mat the scales on wool fibers until they lock together, which is why a hot machine cycle turns a fitted sweater into a dense, shrunken one. Superwash treatment resists this by stripping or coating those scales, which is exactly why it survives the gentle cycle that untreated merino does not. The second is stretching, and it is a drying problem rather than a washing one: a wet knit hung from its shoulders distorts under its own weight, so every wool sweater dries flat regardless of fiber. Moths are the third threat, and they target protein fiber specifically, which is why sealed off-season storage matters more than any single wash decision.

Matching the fiber to the job

Each of the three fibers earns its keep in a different slot. Cashmere suits low-friction wear — a layering piece under a coat, an evening sweater — where its warmth-to-weight justifies hand washing and careful storage, and where nothing rubs against it hard enough to exploit that short staple. Merino is the working fiber: base layers, travel knits, anything worn against skin on a schedule, because the long staple holds a surface through friction and the superwash versions survive real laundry. Lambswool is the warmth-first pick, springy and loft-warm, best in pieces where softness against bare skin is not the point. A sweater worn weekly needs the durability argument; a sweater worn monthly can afford the delicacy. The guide to caring for cashmere covers the washing routine in detail, and the pilling guide extends the staple-length mechanics above. For blends, wool care basics cover what the label leaves out.

More fiber and fabric explainers live in the site’s apparel section, and the guides hub collects the care and construction topics in one place.