Knitting

In short

Knitting makes fabric by intermeshing loops of yarn, either across the width (weft knitting) or down the length (warp knitting), so the fabric stretches, recovers and conforms to the body without any yarn being under tension in a crossed-over structure. It is the second major fabric-formation route after weaving and dominates T-shirts, innerwear, socks, sportswear, fleece, shoe uppers and technical textiles such as warp-knit geogrids and medical meshes. In Indian university syllabi it is examined as loop geometry, machine mechanisms (needle–cam–sinker action), structure analysis, GSM/stitch-density calculation and defects; GATE (TF paper) asks loop length, tightness factor, course–wale density and production calculation. Employers who test it directly include the Tirupur and Ludhiana knitwear cluster, Shahi Exports, Arvind, KPR Mill, Page Industries (Jockey), Trident, Welspun and machine suppliers like Mayer & Cie, Santoni, Karl Mayer, Terrot and Shima Seiki agents.

Explained

Fundamentals, elements and geometry

• Knitting: fabric formation by intermeshing loops; one yarn can in principle make a whole fabric (weft knitting), unlike weaving which needs two yarn sets.
• Loop (stitch): basic unit — a head (needle loop), two legs, and two feet joining into the sinker loop of the course below.
• Course: a row of loops across the fabric width (horizontal); Wale: a column of loops along the length (vertical). Courses per cm (CPC) and wales per cm (WPC) define fineness.
• Stitch density S = CPC × WPC (loops/cm²). Loop length ℓ: length of yarn in one loop (mm) — the single most important parameter; it fixes dimensions, GSM and handle.
• Face loop (knit): legs of the new loop lie over the old loop, showing a V on the technical face. Reverse loop (purl): the loop head shows, giving a semicircle.
• Technical face / technical back: defined by how the fabric lay on the machine, not by which side is used in the garment.
• Three stitch types: knit (loop), tuck (yarn held in needle hook without knocking over — wider, thicker, lower extensibility lengthwise), miss/float (needle not raised; yarn floats behind — narrower, less extensible widthwise, lower GSM than knit).
• Gauge (gg): needles per inch of needle bed. Common weft gauges: E18–E28 for fine single jersey, E12–E14 for rib, 3–12 gg for flat-bed sweaters. Needle pitch = 1/gauge.
• Machine diameter for circular machines in inches; total needles = π × diameter × gauge.
• Feeders: number of yarn feeds = number of courses produced per machine revolution.

Needles, cams, sinkers and loop formation

• Needle types: latch (tongue) needle — hook plus pivoted latch, used in almost all weft knitting; bearded (spring) needle — needs a presser, used in some warp-knit and hosiery machines; compound (two-part/slider) needle — shortest stroke, highest speed, standard on modern warp-knitting machines.
• Weft loop-formation sequence (latch needle): 1) rest/clearing — needle rises, old loop slides below the open latch onto the stem; 2) yarn feeding — new yarn laid in the hook as the needle descends; 3) latch closing — old loop closes the latch; 4) landing — old loop sits on the closed latch; 5) knock-over (cast-off) — old loop is cast over the hook, new loop drawn through it; 6) loop length set by cam depth (stitch cam setting).
• Cams: knitting cam (clearing + stitch cam), tuck cam (raises needle part way — tuck), and miss cam (needle stays down — float). The cam system (feeder station) is one complete set; number of feeders = number of cam systems.
• Sinkers (on single-jersey machines) hold, support and knock over the loop while the needle rises; on double-jersey machines the opposing bed performs this function.
• Needle selection for patterning: cams and tricks (butt arrangement), pattern wheel, jacquard drums, punched tape, and electronic needle selection (piezoelectric/electromagnetic actuators) on modern jacquard and seamless machines.
• Take-down and quality control: positive/negative yarn feed, yarn tension (storage feeders), stitch cam depth, fabric take-down tension — these four set loop length and hence GSM.

Weft knitting: structures and machines

• Yarn runs across the fabric (course-wise); made on circular (tubular or open-width via slitting) and flat-bed V-bed machines, plus hosiery and glove machines.
• Four primary weft bases:
  1. Plain / single jersey — one needle bed, all face loops on one side. Light, most extensible, highest curling and laddering (runs); curls to the face at top/bottom edges and to the back at the sides. Unroving possible from the last-knitted course only.
  2. Rib (1×1, 2×2, etc.) — two beds, needles in rib (alternate) gating; face and reverse wales alternate. Twice the thickness of jersey at the same loop length, excellent widthwise elasticity and recovery, does not curl, used for cuffs, collars, waistbands.
  3. Interlock — two 1×1 ribs interlocked, needles in interlock gating (long/short needles on both beds); dimensionally stable, smooth both sides, heavier; used in polo shirts, innerwear.
  4. Purl (links-links) — alternate courses of face and reverse loops; maximum lengthwise extensibility; made on double-cylinder or V-bed machines with transfer; used in socks welts, sweaters.
• Derivatives: single piqué/cross tuck (tuck based, lacoste), honeycomb, fleece (two- or three-thread with laying-in yarn), terry/plush (sinker loop pulled long), French terry, single jersey with elastane (plating), ponte/ponti di roma, half-cardigan and full cardigan (rib + tuck), milano and half-milano rib, eight-lock, 1×1 and 2×2 variations.
• Other weft features: plating (two yarns fed so one shows on face — used for elastane and melange effects), inlay/laying-in (yarn not knitted, only trapped — fleece, body-size elastics), intarsia, striping (feeder striping with electronic yarn fingers), pointelle (loop transfer to make holes), racking (bed shift for cables).
• Machine families: single-jersey circular (30″–38″, E24–E28, 2–4 feeders per inch of diameter); double-jersey rib/interlock machines; body-size and seamless machines (Santoni) for tubular garments; flat-bed computerised (Shima Seiki, Stoll) with full-fashion shaping and complete-garment / WholeGarment knitting; circular sock machines and double-cylinder machines.

Warp knitting: structures and machines

• Yarn runs along the fabric; a whole warp sheet from a beam is fed, one or more threads per needle, all needles knit simultaneously — the fastest fabric-forming method (courses/min in thousands).
• Elements: compound needles in a bar, guide bars (one guide per needle per bar) carrying the warp, sinker bar, trick plate. Motion per course: swing to the back → overlap shog → swing to front → underlap shog → knock-over. Overlap forms the loop; underlap connects wales and carries most of the yarn.
• Chain notation: guide-bar movement written as needle-space numbers, e.g. 1-0/1-2// (tricot), 1-0/2-3// (locknit-type 2-bar), 1-0/0-1// (pillar/chain stitch, needs a second bar or inlay to hold together).
• Tricot machine: 2–4 guide bars, compound needles, high speed, light fabrics — locknit (front bar 1-0/2-3, back bar 1-2/1-0) is the workhorse for linings, lingerie, swimwear; sharkskin, queenscord, satin (long underlap).
• Raschel machine: many guide bars (up to 70+), latch needles, vertical take-down, patterned and open structures — lace, curtains/net, elastic nets, geogrids, spacer fabrics (double-needle-bar raschel for 3-D spacer and tubular medical grafts).
• Other warp-knit routes: weft-insertion warp knit, warp-knit terry, Co-we-nit, and stitch-bonding (Malimo/Maliwatt) which stitches a web or yarn layer and is treated under nonwoven-reinforcement lines.
• Advantages: very high output, no twist-related spirality, run-resist, can be made nearly non-stretch with long underlaps; limitations: needs warping (beam preparation), little flexibility for short runs, less soft handle than weft knits.

Dimensional behaviour, properties and comparison

• Loop-length dominance (Munden): for relaxed plain knit, course and wale densities depend only on loop length, not on yarn count or machine gauge — hence the dimensionless constants Kc, Kw, Ks, Kr.
• Tightness factor (K or TF) = √tex / ℓ — measures how tight the structure is; typical single jersey 1.3–1.5 (cotton), rib ~1.3–1.6. Too low → slack, baggy, low cover; too high → stiff, high knitting tension, needle breakage.
• Shrinkage and relaxation: dry relaxed → wet relaxed → fully relaxed (tumble) states; knits shrink mainly in length. Compaction/finishing (steam, compactor) is used to pre-set dimensions; residual shrinkage limits are usually specified by the buyer (commonly ±3–5% after specified wash), tested by IS 2977 / ISO 6330 + ISO 5077-type procedures.
• Spirality: wales lean away from vertical in single jersey because of yarn twist torque; worse with higher twist multiplier, finer gauge-to-count mismatch, single yarns, and multi-feeder machines. Reduced by low-twist/compact or two-ply yarn, balanced twist direction (Z yarn on a particular machine rotation), heat-set polyester blends and proper compacting.
• Curling at edges of single jersey; laddering (one broken loop runs down a wale); unroving from the knitted end.
• Properties versus woven: higher extensibility (20–200% vs 2–10%), better recovery, higher air permeability and bulk, superior crease recovery and drape, but lower dimensional stability, lower bursting-type strength per unit mass, higher shrinkage and snagging tendency.
• Key quality tests: GSM (IS 1964 for mass per unit area of fabric), thickness (IS 7702-type), bursting strength (ball burst / diaphragm, not tensile strip for knits), pilling (ICI pilling box / Martindale), dimensional change on washing, spirality, courses/wales per cm, CAF (cover factor), and loop length by yarn-unroving (course-length method).
• Standards and compliance practice (India): BIS has standards on knitted fabric terminology, mass per unit area, dimensional change and test methods; many older knitwear IS numbers have been revised or withdrawn, so confirm the current number and year before quoting. Textile product safety is mostly buyer- and regulation-driven: GOTS/OEKO-TEX certification for exports, Quality Control Orders notified for some textile items, BIS mandatory marking applies to certain products only. Export incentives run through RoSCTL/RoDTEP and schemes such as PM MITRA parks; knitwear and knitted garments are in the 5% GST slab for garments priced up to ₹2,500 and 18% above that, with man-made fibre/yarn rationalised to 5% from 22 September 2025 (GST slabs are now 5%/18%/40%). Factory operations are governed by the four Labour Codes in force from 21 November 2025, which replaced the Factories Act and the Minimum Wages, Industrial Disputes and BOCW Acts.

Faults, causes and process control

• Needle line / vertical line: bent, worn or broken needle hook/latch → replace needle; check needle gating.
• Hole / drop stitch: yarn breakage, high yarn tension, bad knot, weak yarn, wrong latch timing.
• Barré / horizontal streaks: mixed yarn lots, count/twist/dye-affinity variation between feeders, uneven feeder tension.
• Fly / lint and oil stains: poor blowing/suction, over-lubrication, dirty cam box; a major cause of Tirupur rejections.
• Press-off: all loops lost from needles due to fabric take-down failure or yarn run-out.
• Spirality, snagging, pilling, crack marks, tuck/float misplacement from wrong cam or needle selection.
• Control levers: positive storage feeders for constant yarn input, loop-length meters, on-line fabric inspection, fixed stitch-cam setting, same lot yarn to all feeders, controlled relative humidity (about 60–65% RH, 25–30 °C in the knitting hall), yarn waxing for low friction.

Key points

• Knitting - intermeshing of loops; weft = yarn across courses, warp = yarn along wales.
• Course / wale - horizontal row / vertical column of loops; CPC × WPC = stitch density.
• Loop length ℓ - yarn length per loop; controls GSM, dimensions and handle more than any other variable.
• Stitch types - knit, tuck (wider, thicker), miss/float (narrower, lighter).
• Latch needle - universal in weft knitting; compound needle - standard in warp knitting; bearded needle needs a presser.
• Knitting cycle - clearing, yarn feed, latch closing, landing, knock-over.
• Gauge - needles per inch; total needles = π × diameter(inch) × gauge.
• Four primary weft structures - plain (single jersey), rib, interlock, purl.
• Single jersey - curls, ladders, most extensible; rib - no curl, best widthwise stretch; interlock - most stable, heaviest.
• Plating - two yarns fed together so one covers the face; used for elastane and melange.
• Warp knitting - tricot (2–4 bars, fast, locknit) and raschel (many bars, lace, nets, spacers).
• Chain notation - 1-0/1-2// tricot, 1-0/2-3// locknit front bar, 1-0/0-1// pillar.
• Overlap forms loops; underlap links wales and consumes most yarn.
• Tightness factor K = √tex / ℓ (mm) - typical 1.3–1.5 for single jersey.
• Munden constants - Kc = CPC×ℓ, Kw = WPC×ℓ, Ks = S×ℓ², Kr = Kc/Kw; dimensionless for relaxed plain knit.
• Spirality - twist-induced wale lean in single jersey; cured by low-twist/plied/compact yarn and compacting.
• Bursting strength, not tensile strip strength, is the right strength test for knits.
• Production = machine rpm × feeders × needles × loop length - the basis of all output calculations.

Formulas and examples

Example 1 — Needles, loops and stitch density. A single-jersey circular machine: D = 30″, G = 24 gg, 90 feeders, 24 rpm.

• N = π × 30 × 24 = 2,261 needles (2,261.9 → 2,261 in practice).
• Loops per revolution = 2,261 × 90 = 203,490 loops.
• Courses per minute = 24 × 90 = 2,160 courses/min.
• If CPC = 18 courses/cm, fabric length rate = 2,160 / 18 = 120 cm/min = 72 m/h (tubular).

Example 2 — GSM from loop length and count. Cotton 30s Ne single jersey, ℓ = 3.0 mm, CPC = 18, WPC = 14.

• tex = 590.5 / 30 = 19.68 tex.
• S = 18 × 14 = 252 loops/cm².
• Yarn length per cm² = 252 × 0.30 cm = 75.6 cm = 0.756 m.
• Per m² = 0.756 × 10,000 = 7,560 m.
• Mass = 7,560 m × 19.68 g/1000 m = 148.8 g/m² ≈ 149 GSM.
• Check by formula: 18 × 14 × 3.0 × 19.68 / 1000 = 148.8 ✓.

Example 3 — Tightness factor and Munden constants. Same fabric as Example 2: tex = 19.68, ℓ = 3.0 mm.

• K = √19.68 / 3.0 = 4.436 / 3.0 = 1.479 — a normally tight single jersey (typical 1.3–1.5).
• Kc = 18 × 0.30 cm = 5.4 (using ℓ in cm, CPC in /cm); Kw = 14 × 0.30 = 4.2; Ks = 5.4 × 4.2 = 22.7; Kr = 5.4/4.2 = 1.29.
• Fully relaxed plain-knit reference values are about Kc ≈ 5.3, Kw ≈ 4.1, Ks ≈ 21.6, Kr ≈ 1.29 — so this fabric is close to fully relaxed, i.e. little further shrinkage is expected. (Published constants vary a little between sources and relaxation treatments.)

Example 4 — Production and efficiency. Machine of Example 1 (2,261 needles, 90 feeders, 24 rpm) knitting ℓ = 3.0 mm, 19.68 tex, efficiency 85%, 8-hour shift.

• Loops per minute = 203,490 loops/rev × 24 rpm = 4,883,760 loops/min.
• Yarn length per minute = 4,883,760 × 3.0 mm = 14,651,280 mm = 14,651 m/min.
• Mass per minute = 14,651 × 19.68 / 1000 = 288.3 g/min.
• Theoretical = 288.3 × 60 = 17,298 g/h ≈ 17.30 kg/h.
• At 85% → 14.70 kg/h → 117.6 kg per 8-h shift per machine.
• A 40-machine hall → about 4,705 kg/shift ≈ 14,115 kg/day on three shifts (before grey-fabric waste of about 2–3%).
• Cross-check with Example 1: 72 m/h tubular × (2 × 0.808 m) × 149 g/m² ≈ 17.3 kg/h ✓.

Example 5 — Fabric width and count change. Same machine, WPC = 14 wales/cm.

• Open width = 2,261 / 14 = 161.5 cm; tube (flat) width = 80.8 cm, i.e. about 31.8″ — slightly wider than the 30″ cylinder, as expected after relaxation.
• If the yarn is changed to 40s Ne (tex = 590.5/40 = 14.76) at the same loop length and densities, GSM = 18 × 14 × 3.0 × 14.76 / 1000 = 111.6 GSM — lighter fabric, and K falls to √14.76/3.0 = 1.28, i.e. a slacker structure, so the stitch cam must be tightened (lower ℓ) to keep the same handle.

Where it is used

• Knitwear clusters: Tirupur (cotton T-shirts and innerwear, India's largest knitwear export hub), Ludhiana (woollen and acrylic sweaters, flat-bed), Kolkata and Delhi-NCR for hosiery and fashion knits.
• Large Indian manufacturers: KPR Mill, Shahi Exports, Arvind, Page Industries (Jockey), Trident, Welspun, Dollar and Rupa (vests, briefs — single jersey and rib), Gokaldas Exports.
• Technical and industrial warp knits: geogrids and geotextiles for highways (NHAI projects), agro-shade nets, mosquito nets, car seat upholstery and headliners, spacer fabrics for mattresses and shoe uppers (Flyknit-type), surgical meshes and vascular grafts.
• Sportswear and footwear: seamless body-size knitting (Santoni), engineered knit uppers, compression wear with elastane plating.
• Job roles: knitting supervisor/master, PPC and production planning, process and quality engineer (GSM, shrinkage, spirality audits), merchandiser costing fabric from GSM and consumption, R&D/CAD designer on Shima Seiki or Stoll, machine service and application engineer with Mayer & Cie, Terrot, Karl Mayer, Santoni and Pailung agents.
• Research and testing: SITRA (Coimbatore), ATIRA, NITRA, textile committee labs and BIS-recognised labs for buyer-protocol knit testing.

Interview questions

• Q: What is the difference between weft and warp knitting? A: In weft knitting a single yarn runs across the fabric forming successive courses and needles knit one after another; in warp knitting a whole warp sheet runs along the fabric and all needles knit simultaneously, giving much higher speed and a run-resist fabric.
• Q: Which single parameter controls knitted fabric GSM the most, and how do you change it on the machine? A: Loop length — adjusted by the stitch-cam (knock-over cam) depth together with yarn input tension from the positive feeders; deeper cam means longer loop, lower courses per cm and lower GSM.
• Q: Why do you use bursting strength instead of tensile strength for knits? A: A knit is a looped, highly extensible structure, so a strip tensile test mostly measures loop straightening and gives misleading results; a multi-directional ball-burst or diaphragm test reflects how the fabric actually fails in use.
• Q: What causes spirality in a single-jersey T-shirt and how do you reduce it? A: Residual twist torque in the yarn makes wales lean; reduce it with lower twist multiplier, two-ply or compact/vortex yarn, matching yarn twist direction to machine rotation, and heat-setting or compacting in finishing.
• Q: Explain the knitting cycle of a latch needle. A: Clearing (needle rises, old loop slips below the open latch), yarn feeding into the hook, latch closing by the rising old loop, landing of the old loop on the closed latch, and knock-over where the old loop is cast off and the new loop drawn through it.
• Q: What are tuck and float stitches and how do they change the fabric? A: A tuck holds the yarn in the hook without knocking over, making the fabric wider, thicker and heavier with less lengthwise stretch; a float leaves the yarn behind unknitted needles, making the fabric narrower, lighter and less extensible widthwise.
• Q: How many needles are on a 34-inch, 28-gauge machine? A: π × 34 × 28 ≈ 2,991 needles.
• Q: Why does rib fabric not curl while single jersey does? A: Rib has alternating face and reverse wales so the curling forces of the face and reverse loops balance; single jersey has all loops the same way, so unbalanced bending moments curl the edges.
• Q: What is plating and where is it used? A: Feeding two yarns so one consistently lies on the face and the other on the back — used to put elastane or a softer/coloured yarn on one side, as in stretch single jersey and inner-face cotton polyester fabrics.
• Q: What does chain notation 1-0/2-3// mean? A: A guide bar overlapping between needle spaces 1 and 0 on one course and 2 and 3 on the next — a two-needle-space underlap, typical of the front bar of locknit.
• Q: Why is interlock more dimensionally stable than single jersey? A: Its two interlocked 1×1 ribs lock the loops in both directions and the structure is balanced front to back, so the loops have little freedom to redistribute during relaxation.
• Q: A buyer rejects fabric for horizontal streaks across the full width. What do you check first? A: Barré — mixed yarn lots or count/twist/dye-affinity variation between feeders and uneven feeder tension; check yarn lot traceability per feeder, feeder tension and stitch-cam uniformity.
• Q: Why is knitting generally cheaper per metre than weaving? A: It needs no sizing or warping for weft knits, converts cone yarn to fabric in one step with few preparatory processes, and runs at high loop-formation rates with low yarn tension and less waste.

Common mistakes

• Mixing units in GSM calculation — using ℓ in mm with S in loops/cm² without the /1000 factor, or confusing tex with Ne (tex = 590.5/Ne, not 1000/Ne for cotton counts).
• Treating gauge as needles per cm; it is needles per inch, and total needles must use diameter in inches.
• Calling the technical face the "right side" of the garment — the face is defined by the machine, not by the garment design.
• Confusing course and wale, or multiplying CPC × WPC and calling it GSM; stitch density is loops/cm², not mass.
• Forgetting that courses per minute = rpm × feeders, and dividing by feeders instead of multiplying in production sums.
• Reporting theoretical production as actual — machine efficiency (typically 80–90%) and waste must be applied.
• Saying a tuck makes a fabric narrower (it widens it) and a float wider (it narrows it) — the two are commonly swapped.
• Assuming Munden constants apply to rib or interlock or to a dry-relaxed sample; they are for relaxed plain knit, and values vary with relaxation treatment.
• Quoting withdrawn or superseded IS numbers for knitted goods without checking the current edition.

Related topics

Weaving · Nonwovens · Yarn manufacture and count systems · Textile testing and quality control · Knitted garment manufacturing and CAD · Dyeing and finishing of knitted fabrics