How Is Wool Processed? A Textile Expert’s Step-by-Step Guide

Imagine holding two identical-looking wool suiting fabrics: one drapes like liquid silk, holds crisp tailoring for three seasons, and resists pilling at ASTM D3776 Class 4; the other pills after three dry cleanings, loses shape in humidity, and shows visible fiber migration at the lapel. The difference isn’t design—it’s how is wool processed. As a mill owner who’s overseen over 27,000 tonnes of Merino, Shetland, and crossbred wool since 2006, I can tell you: every decision from scouring temperature to combing tension alters hand feel, drape, GSM, and even colorfastness to light (AATCC Test Method 16E). Get the process right—and your garment performs. Get it wrong—and even the finest Italian cut can’t save it.

From Fleece to Fiber: The Raw Material Matters First

Wool processing doesn’t begin in the mill—it begins in the pasture. The quality, length, crimp, and micron count of raw fleece dictate everything that follows. We source exclusively from farms certified under the Responsible Wool Standard (RWS) or Global Organic Textile Standard (GOTS), because ethical animal welfare directly impacts fiber integrity. A stressed sheep produces brittle, uneven fibers—leading to excessive breakage during carding and lower yarn strength (Ne 60–80 worsted vs. Ne 80–100 achievable with calm, well-fed flocks).

Key metrics we measure pre-processing:

Fiber diameter: 16.5–19.5 microns for superfine Merino; >25 microns for rug wool
Staple length: 75–100 mm ideal for worsted spinning; 45–65 mm for woollen systems
Crimp frequency: 12–16 waves per cm indicates high elasticity and resilience
Yield after scouring: Typically 45–70%—meaning 100 kg raw fleece yields just 45–70 kg clean wool, depending on grease content (lanolin %)

"Scouring isn’t cleaning—it’s selective dissolution. Remove too much lanolin, and fibers become brittle and static-prone. Remove too little, and dye uptake suffers, especially in reactive dyeing systems." — Dr. Elena Rossi, Textile Chemist, Biella Wool Institute, 2022

Step 1: Scouring – Removing Grease Without Sacrificing Integrity

Raw wool contains up to 40% impurities: lanolin (wool grease), suint (dried sweat salts), dirt, vegetable matter, and pesticide residues. Scouring removes these—but how it’s done determines fiber softness, tensile strength, and environmental compliance.

We use a low-temperature, pH-controlled continuous scouring line (55–60°C, pH 9.2–9.6) with biodegradable anionic surfactants meeting OEKO-TEX Standard 100 Class I requirements. Why not hotter? Because temperatures above 65°C denature keratin proteins—reducing elongation-at-break by up to 22% (ISO 105-E01 data). Our scouring yield averages 58%, with residual lanolin held at 0.3–0.7%—just enough to lubricate fibers during drafting but low enough for uniform reactive dye penetration.

Scouring Methods Compared

Carbonising: Used only for fleeces with heavy burr/seed contamination. Involves sulphuric acid dip + controlled baking. Risk: weakens fibers if acid concentration exceeds 120 g/L.
Enzyme scouring: Emerging alternative using alkaline proteases. Reduces water use by 35% and energy by 28%, but requires precise pH/temp control (60°C, pH 8.5) to avoid hydrolysis.
Solvent scouring: Rare for apparel wool—used only in technical applications where zero water footprint is mandated (e.g., GRS-certified military uniforms).

Step 2: Sorting & Grading – Where Value Is Locked In

This is where mills separate commodity from craft. Skilled graders—many trained for 10+ years—hand-sort fleece by region of the sheep, not just micron. The shoulder and midside yield the longest, most parallel fibers (ideal for worsted); britch and belly are shorter, more irregular (best for woollen felts or insulation).

We grade against International Wool Textile Organisation (IWTO) standards, measuring:

Evenness: Assessed via Uster AFIS (Advanced Fibre Information System)—target CV% ≤ 18%
Medullation: Hollow core presence (>5% medullated fibers = downgraded for apparel)
Vegetable Matter (VM): Must be <2.0% for GOTS certification; removed mechanically post-scouring via double-deck shakers and air-lift separators

Post-grading, fibers are baled at 250–300 kg, pressed to 350–400 kPa, and stored in climate-controlled warehouses (RH 65%, 18°C) to prevent moisture regain fluctuations before processing.

Step 3: Carding & Combing – Aligning the Future of Your Fabric

Carding opens, cleans, and aligns fibers into a loose web called a sliver. Combing—optional but critical for worsted wool—removes short fibers (<25 mm) and further straightens staples. This step defines your fabric’s ultimate performance ceiling.

Carding: Woollen vs. Worsted Paths

Woollen system: Uses drum carders with fine wire clothing (120–180 points/cm²). Produces airy, bulky slivers with random fiber orientation → ideal for brushed flannels (GSM 280–320), melton cloths, and felted outerwear. Yarn count range: Ne 16–32.
Worsted system: Employs high-speed roller carders + gill boxes, followed by combing (using French or Noble combs). Removes all fibers under 38 mm, yielding parallel, dense slivers → essential for sharp suiting (GSM 240–290), gabardines, and crepe de chine wools. Yarn count range: Ne 60–100+.

Combing efficiency directly impacts pilling resistance. Our combed worsted slivers achieve AATCC Test Method 135 Class 4–5 after 20 washes—uncombed equivalents rarely exceed Class 2. Why? Short fibers migrate to the surface and entangle. Remove them early; solve the problem forever.

Step 4: Spinning – From Sliver to Strength

Spinning converts sliver into yarn—with dramatic implications for fabric hand, drape, and durability. We operate both ring and compact spinning frames, but for premium wool, we prefer compact spinning: it reduces hairiness by 35% and increases tenacity by 12% versus traditional ring-spun.

Key parameters we lock in:

Twist multiplier (TM): 3.8–4.2 for worsted suiting (higher TM = stiffer hand, better abrasion resistance)
Yarn count: Ne 70–80 for lightweight summer suits; Ne 48–56 for winter coatings
Twist direction: Z-twist for warp yarns (adds strength); S-twist for weft (improves weft insertion in rapier weaving)
Evenness (CV%): Target ≤ 12.5% per Uster Tester 6—critical for digital printing clarity and reactive dye uniformity

For stretch wool blends, we integrate spandex filaments (2.2–4.4 dtex) at 3–5% during spinning—not post-weave. This ensures consistent recovery (≥92% after 10,000 cycles, per ASTM D2594) and eliminates torque distortion in cut panels.

Step 5: Weaving & Knitting – Building the Fabric Architecture

Wool’s natural resilience makes it exceptionally versatile across loom types—but each method delivers distinct structural benefits.

Weaving Systems for Wool

Rapier weaving: Our go-to for complex twills and herringbones (e.g., 2/2, 3/1, houndstooth). Achieves fabric widths up to 170 cm, selvedge stability ±0.5 mm, and weft density up to 42 picks/cm. Ideal for suiting with warp: Ne 70, weft: Ne 60.
Air-jet weaving: Used for high-volume plain weaves (poplins, gabardines). Speeds up to 1,200 ppm—but limited to yarns ≥Ne 50 due to fiber fly-off risk.
Warp knitting (Raschel): For structured wool lace, jacquard mesh, or bonded interlinings. Enables precise grainline control—critical for bias-cut dresses where drape must flow exactly 45° off the selvage.

Circular Knitting for Wool

We use fine-gauge circular machines (24–32 needles/inch) for lightweight wool jerseys (GSM 180–220). Key advantage: inherent 4-way stretch without spandex—thanks to wool’s crimp recovery. But beware: loop length must be tightly controlled (1.8–2.2 mm) to prevent ladder runs. Our best-selling Merino jersey passes AATCC Test Method 147 (snag resistance) Grade 4.

Step 6: Finishing – Where Character Is Sealed

This is where wool transforms from textile to signature. Finishing isn’t cosmetic—it’s functional engineering.

Core Finishing Techniques & Their Impact

Felting (fulling): Controlled shrinkage (8–12% in width, 5–8% in length) via heat, moisture, and agitation. Creates dense, wind-resistant cloth (e.g., boiled wool, GSM 380–450). Over-felting destroys drape—our lab tests ensure dimensional change stays within ISO 105-C06 tolerances.
Decating: Steam-heated rollers apply 2–3 bar pressure for 30 seconds. Sets twist, improves luster, and stabilizes grainline—essential before cutting. Reduces seam slippage by 40% (ASTM D434).
Enzyme washing (Protease-based): Softens hand without fiber damage. We use EC 3.4.21.62-certified enzymes at 50°C, pH 7.5, for 45 minutes—resulting in 22% softer handle (Kawabata Evaluation System) and zero weight loss.
Superwash treatment: Chlorine-Hercosett process (per ISO 3071) followed by polymer resin coating. Enables machine-washability—but reduces natural breathability by ~18%. Not recommended for performance outerwear.

Dyeing & Printing Precision

We exclusively use reactive dyeing for wool-acrylic blends (excellent wash fastness, AATCC 61-2A ≥4) and acid dyeing for 100% wool (superior levelness, ISO 105-X12 grey scale ≥4.5). For digital printing, pretreatment is non-negotiable: we apply cationic fixatives to boost ink fixation—achieving ISO 105-B02 lightfastness ≥6 on wool crepe.

Wool Fabric Type	Typical GSM	Warp/Weft Count (Ne)	Best Applications	Pilling Resistance (AATCC 135)	Drape Coefficient (%)
Merino Worsted Suiting	240–290	70/60	Jackets, trousers, structured dresses	Class 4–5	38–42
Shetland Tweed (Woollen)	310–360	32/32	Coats, capes, heritage outerwear	Class 3–4	52–58
Boiled Wool	380–450	N/A (felted)	Winter vests, sculptural skirts, accessories	Class 5	22–28
Wool Jersey (Circular Knit)	180–220	N/A (single knit)	Tops, leggings, layered knits	Class 4	75–82
Wool Gabardine	260–300	64/56	Raincoats, tailored skirts, uniforms	Class 4–5	44–48

Care & Maintenance: Protecting Your Wool Investment

Wool’s longevity isn’t automatic—it’s earned through intelligent care. Here’s what our R&D lab and 18 years of mill-floor experience confirm works:

Storage: Always fold—not hang—wool suiting. Hangers distort shoulders and stretch the warp. Use acid-free tissue and cedar-lined drawers (not mothballs—naphthalene damages keratin).
Cleaning: Dry clean only with hydrocarbon solvents (not perc—banned under REACH Annex XVII). For wool jerseys: cold hand-wash with pH-neutral detergent (ISO 6330 compliant), lay flat to dry away from direct sun (UV degrades cystine bonds).
Steam vs. Iron: Use steam only—never dry iron wool. Set steam iron to “wool” (148°C max) and press with a damp cotton press cloth. Excessive heat causes fiber yellowing (AATCC Test Method 18).
Pilling: Use a battery-powered fabric shaver (not a razor—too aggressive). Frequency? Every 3–4 wears for high-friction zones (underarms, cuffs).
Colorfastness: Avoid chlorine bleach at all costs. Even diluted, it causes irreversible yellowing and strength loss. For stain removal, use 3% hydrogen peroxide on white wool only—test first.

Design & Sourcing Tips You Won’t Find on Data Sheets

As someone who’s reviewed over 14,000 fabric submissions for brands like Loro Piana, Arket, and Patagonia—I’ll share what moves the needle:

Ask for the scouring report: Not just “clean wool”—demand residual lanolin %, VM %, and pH of final rinse. If they won’t share it, walk away.
Test drape before cutting: Hold fabric 30 cm from chin, let fall naturally. True worsted should form 3–4 smooth folds—not stiff V-shapes (over-combed) or chaotic ripples (under-carded).
Check selvedge integrity: Run your thumb along the edge. It should feel tight, even, and slightly raised—not fuzzy or frayed. Poor selvedge = unstable grainline = distorted hems.
For digital prints: Specify pre-treated wool, not “print-ready.” Untreated wool absorbs ink unevenly—causing haloing on fine lines. Our pretreatment adds 5% weight but guarantees ISO 105-J03 registration accuracy ±0.15 mm.
Stretch wool? Demand recovery % after 10,000 cycles—not just “4-way stretch.” And verify spandex is core-spun, not wrapped.