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WITHIN · FIELD GUIDE · Revised November 5, 2026

Types of wool: merino, cashmere, tweed and Super 100s

One number sorts every wool on a label: how thick the fibre is. The thinner it is, the softer it feels and the faster it wears.

The fibres, by width

FibreFromWidth in micronsWhat it is good at
Ultrafine merinoMerino sheep11.5 to 15Next to skin base layers, fine suiting
Superfine merinoMerino sheep15 to 18.5Fine knits and suits
Fine merinoMerino sheep18.6 to 20.9Everyday sweaters
Medium and strong merinoMerino sheep21 to 24.5Hard wearing knits and coats
CashmereCashmere goat undercoat19 or finer on average, by US lawWarmth for its weight, softness
AlpacaAlpacaAbout 18 to 25, for good fibreWarm, smooth, little lanolin
MohairAngora goatAbout 25 to 45Sheen, strength, a hairy halo
LambswoolA sheep's first shearingVaries by breedSoft, elastic knits

On an American label, cashmere has a legal meaning: the fine dehaired undercoat of the cashmere goat, averaging no more than 19 microns. No more than 3 percent of the fibre may be over 30 microns.

Super 100s and the numbers on suits

The S number comes from the International Wool Textile Organisation's code, and it is a maximum fibre width measured on the finished cloth. Higher is finer, softer and more delicate. A Super 180s suit feels soft and creases faster. For a suit you wear every week, I'd stay between 100s and 130s.

LabelFibre no wider than
Super 80s19.75 microns
Super 100s18.75 microns
Super 110s18.25 microns
Super 120s17.75 microns
Super 130s17.25 microns
Super 150s16.25 microns
Super 180s14.75 microns

Cloths that are not a fibre

Tweed is a rough woollen cloth, woven plain, in twill or in herringbone. Harris Tweed is the one with a law behind it. The Harris Tweed Act 1993 says it is handwoven by islanders at their homes in the Outer Hebrides, from pure virgin wool dyed and spun there.

Boiled wool starts as a knit and is agitated in hot water until it shrinks into a dense felt that does not fray. Both are about how the cloth is made, so either can be any grade of wool.

Checks on a label

  • Read the fibre content line, not the name. "Cashmere feel" is not cashmere.
  • A Super number on a blend is allowed only with the word Super dropped, and at least 45 percent wool.
  • A Harris Tweed label carries the Orb mark.
  • For a sweater you will wash at home, merino forgives more than cashmere. The washing guide has the routine for both.

Wool on within

Merino, cashmere and tweed in stock at the boutiques today, with their prices.

Common questions

Is merino wool better than cashmere?
Different, not better. Fine merino can be as thin as cashmere: superfine merino runs 15 to 18.5 microns, and US law caps cashmere at an average of 19. Cashmere is softer and loftier for its weight; merino is tougher, cheaper and easier to wash.
What does Super 100s mean on a suit?
The wool's fibres average 18.75 microns or finer. Each step of ten is half a micron finer: Super 120s is 17.75, Super 150s is 16.25. Finer cloth feels softer and wrinkles and wears faster.
What is tweed?
A rough, thick woollen cloth, woven plain, in twill or in herringbone. Harris Tweed is a name protected by the Harris Tweed Act 1993. It is handwoven by islanders at home in the Outer Hebrides, from pure virgin wool dyed and spun there.
What is boiled wool?
Knitted wool agitated in hot water until it shrinks and felts. The result is dense, windproof and does not fray, which is why it is used for coats, jackets and slippers.
What is lambswool?
Wool from a sheep's first shearing, at around seven months, with fibres 50 millimetres or shorter. It is softer and more elastic than wool from older sheep.

Sources

Wool in stock now, to check against this guide

Giovanni Cavagna, INTO THE EAST, Baracuta and more, from the boutiques on within.