Yarn Specifications: Which Yarn Properties to Put in a Bulk RFQ

Three Groups of Yarn Properties

Most items in yarn specifications fall into three groups:

• Physical properties: count (linear density), twist, evenness, hairiness, fiber fineness, fiber density and moisture regain.
• Mechanical properties: breaking strength (tenacity), elongation at break and recovery after stretching.
• Chemical and processing behavior: how the fibers react to light, heat, acids and alkalis during dyeing, finishing and washing.

The fiber family sets much of this, including moisture regain, density and chemical resistance. The spinning route and twist decide most of the rest. A property that cannot be tested gives you little to work with in a quality dispute. So for each item, write four things into your yarn specifications: the target, the tolerance, the test method and the acceptance rule. The sections below name the usual method for each property.

Yarn Count: State the System, the Ply and the Basis

Yarn count describes how fine or coarse a yarn is. The same yarn can be written in several systems, and they do not all run in the same direction:

Unit	What it measures	A higher number means
Ne (English cotton count, often written “S”)	Number of 840-yard hanks per pound	Finer yarn
Nm (metric count)	Kilometres per kilogram	Finer yarn
tex / dtex	Grams per 1,000 m / per 10,000 m	Coarser yarn
Denier (D)	Grams per 9,000 m	Coarser yarn

Useful conversions: Nm ≈ Ne × 1.693, tex = 590.5 ÷ Ne = 1,000 ÷ Nm = denier ÷ 9, and denier ≈ 5,315 ÷ Ne. A 30S cotton yarn, for example, is about Nm 50.8, 19.7 tex or 177 denier.

Two notation habits cause many quoting errors. In the wool and bulky-yarn trade, “1/28” means a single-ply yarn of 28 Nm, but some suppliers write “1/28” or “28S” without saying whether the figure is Ne or Nm. Bulky yarns are also often labeled with two counts, such as 1/28 (1/35) Nm. Here 1/35 is the count as spun and 1/28 is the count after bulking, once the high-shrink fibers have contracted. If you calculate fabric weight from the as-spun count, the result will be about 20% too low.

In your yarn specifications, write the value, the count system, the number of plies and whether the figure describes the single yarn or the resultant plied yarn. Linear density is normally checked with the skein method in ISO 2060. Our guide to denier, yarn count and fabric GSM explains why fabric weight cannot be worked out from the count alone.

Twist, Spinning Method and Hairiness

Twist

Twist holds the fibers together. More twist gives a stronger, crisper and leaner yarn. Less twist gives a softer, fuller hand with less torque, but more pilling. For this reason, knitting yarns are normally spun with lower twist than weaving yarns.

State twist as turns per metre (tpm), turns per inch or a twist factor tied to the count system. Give the direction (S or Z) and agree a tolerance. Around ±5% on the average is a common starting point, measured with a stated method such as ISO 2061 or ISO 17202. High-twist singles in single jersey often cause spirality after washing, so mention the fabric structure in your RFQ. Our article on how twist changes the feel of the same cotton count goes into more detail.

Spinning method

At the same count, the spinning route changes the yarn surface, strength and hairiness:

• Ring: the versatile base method for a wide count range.
• Compact: a cleaner surface, less hairiness and higher strength.
• Siro and compact siro: low hairiness and a ply-like structure.
• Open-end (rotor): economical coarser counts with a bulkier, less regular structure.
• Vortex (MVS): low hairiness and good pilling resistance.

Put the spinning method into your yarn specifications, and for cotton add combed or carded. Two yarns with the same count and blend but different spinning methods will knit and pill differently.

Hairiness

Hairiness is the amount of fiber ends standing out from the yarn surface. It affects pilling, surface clarity, color depth and the amount of fly on the knitting floor. Labs report it as the Uster H index or as a Zweigle S3 count of hairs 3 mm and longer. Compare yarns only on the same instrument and settings. Our article on yarn hairiness and singeing explains how spinning and singeing reduce it.

Strength, Elongation and Evenness

Strength and elongation show up on the knitting machine as end breaks and stops. Ask for single-yarn tenacity in cN/tex and elongation at break, each with its coefficient of variation (CV%). Both should be tested by ISO 2062 or ASTM D2256 at the same gauge length and test speed, and compared at the same count.

Look closely at the minimum values and the CV%. A yarn with a good average and a few very weak places will still break in production. Low minimums and high variation predict end breaks better than the average does.

Evenness is measured on a capacitance tester (for example to ISO 16549 or ASTM D1425). It is reported as the CV% of yarn mass, with imperfections (IPI) counted as thin places, thick places and neps per kilometre. Thin places are weak points. Thick places and neps show on plain knitted surfaces, especially after dyeing. Fiber properties, twist, plying and blend ratio all influence these results, and our article on the main factors affecting yarn strength and elongation covers each one.

Fiber Fineness and Lot-to-Lot Consistency

Fiber fineness controls how many fibers sit in the yarn cross-section. More fibers per cross-section give a more even, stronger yarn and a softer hand. That is why fine counts need fine fibers. When the fiber lot or source changes, fineness can change with it. Buyers notice a different hand feel or a less even surface, even though the count is the same.

To keep repeat orders consistent:

• Give the fiber content with generic names and percentages, and put any trade name next to the generic fiber it refers to.
• Agree a blend tolerance. Many markets, including the EU and the US, allow about 3 percentage points between declared and tested fiber content.
• Ask for upstream information: the fiber producer or source, the fiber type and grade (for example polyester denier and luster) and the spinning mill if it is not the seller. For cotton, HVI data such as staple length, uniformity and micronaire describe the fiber behind the yarn.
• Agree that any change of fiber source is notified and re-approved before bulk shipment.

Moisture Regain, Moisture Content and Wicking

Fibers take up and release moisture from the air all the time. Two measures describe this, and they are easy to mix up:

• Moisture regain = weight of water ÷ oven-dry fiber weight
• Moisture content = weight of water ÷ total weight (fiber plus water)

For example, 100 g of dry cotton holding 8.5 g of water has a regain of 8.5% but a moisture content of about 7.8%.

Fiber	Standard moisture regain
Wool	15%
Linen	12%
Mulberry silk	11%
Lyocell	11%
Cotton	8.5%
Nylon	4.5%
Polyester	0.4%

Standard reference values, for comparison between fibers.

Low-regain fibers such as polyester build up static more easily and can feel stuffy. Regain also affects the invoice. Yarn is commonly traded at a commercial weight, which is the oven-dry weight plus an agreed regain, so state the regain basis for natural and regenerated fibers. For some functions, regain is part of how the yarn works: moisture-absorbing heat-generating viscose releases heat as it binds water vapor.

For quick-dry claims, regain is the wrong number to look at. Polyester absorbs almost no water. Yet profiled polyester with Y-shaped or cross-shaped fibers dries fast, because the grooves carry sweat along the fiber by capillary action. For these products, specify the fiber and its cross-section. Then test the fabric for moisture management (AATCC 195), wicking (AATCC 197 or 198) and drying rate (AATCC 201 or ISO 17617), before and after a set number of washes. Our quick-drying yarn standards guide walks through these tests and their grades.

Fiber Density: Coverage at the Same Fabric Weight

Fiber density is mass per unit volume, and it varies more than many buyers expect. Typical values are about 0.91 g/cm³ for polypropylene, 1.14 for nylon, 1.38 for polyester, 1.52 for viscose and 1.54 for cotton.

At the same GSM, a lower-density fiber gives more volume. A gram of polypropylene fills roughly 1.7 times the space of a gram of viscose, so a knit made with it looks fuller and covers better. This matters for lightweight socks and base layers that must not look sheer. It also explains why two yarns of the same count can give fabrics a different look and hand.

In the spec, describe the result you need: a target GSM plus an approved fabric sample for cover. GSM also depends on knit structure and finishing, so list yarn count and fabric GSM as separate requirements.

Chemical Stability: Match the Spec to Your Dyeing and Finishing Route

Yarn has to survive scouring, dyeing, finishing and repeated washing. Each fiber family has its own weak point:

• Cellulose fibers (cotton, viscose, modal, lyocell) resist alkalis better than acids.
• Protein fibers (wool, silk) resist acids better than alkalis, and alkalis can damage them. Silk is also sensitive to sunlight.
• Synthetic fibers generally resist chemicals well, and polypropylene is known for excellent acid and alkali resistance. Heat is the bigger risk: nylon can yellow or weaken during heat setting, and too much heat degrades spandex.

Your yarn specifications should reflect the real process. Give the supplier the dye class and pH, the maximum dyeing temperature, the heat-setting temperature and dwell time, and any finishes such as softeners or antibacterial treatments. A yarn can look fine in the greige state and fail after finishing, so test strength and appearance on fabric that has been through your full route. When fabric weakens after the stenter, the yarn is not always the cause; our article on fabric strength loss after heat setting explains how to check.

For dyed yarn, agree the colorfastness tests and minimum grades before ordering. The usual set is washing (ISO 105-C06 or AATCC 61), dry and wet rubbing (ISO 105-X12 or AATCC 8), perspiration (ISO 105-E04) and light (ISO 105-B02). Run them on fabric made from the dyed yarn.

How to Write Yarn Specifications for Each Property

Property	What goes wrong if it drifts	What to write in the spec	Usual test
Count	Fabric weight, cover and strength change	Value, count system, ply, tolerance	ISO 2060
Twist	Hand feel, torque, spirality after washing	tpm or tpi, S or Z, tolerance	ISO 2061 / ISO 17202
Tenacity and elongation	End breaks, machine stops, late delivery	Minimum cN/tex, elongation %, CV%	ISO 2062 / ASTM D2256
Evenness and IPI	Cloudy fabric, weak thin places	CV%, thin/thick places and neps per km	ISO 16549 / ASTM D1425
Hairiness	Pilling, fuzz, dull color	Hairiness value on a named instrument	Uster H / Zweigle S3
Fiber blend	Different hand between lots, labeling problems	Generic fiber names, %, tolerance, fiber source	Quantitative fiber analysis (ISO 1833 series)
Moisture regain	Comfort, static, invoiced weight	Regain basis for commercial weight	Oven-dry and conditioned weight
Colorfastness	Fading, staining, returns	Tests and minimum grades	ISO 105-C06, X12, E04, B02

Matching Yarn Specifications to How You Sell

The same yarn can need a slightly different spec depending on where the finished product is sold.

• Wholesalers and distributors: keep one fixed spec sheet for each best-selling item, and ask for lot data with every shipment so that complaints can be traced to a lot.
• Brands (OEM/ODM): every performance claim on a hangtag, such as cooling, quick-dry or antibacterial, needs a test report for that product. Write the test method and the number of washes into the spec.
• Cross-border e-commerce sellers: pilling, bagging and fading are common complaints in customer reviews. Give priority to hairiness and pilling (ISO 12945), elongation and recovery, and colorfastness to washing.
• Supermarkets and mass retail: labeling and paperwork come first. Fiber content must stay within the legal tolerance, and certificates must cover the exact product and still be valid.

Choosing a Functional Yarn for Bulk Production

A functional yarn only pays off if the function survives knitting, finishing and real wear. A practical order of work:

1. Start from the end product and the machine: socks, base layers or knitwear, the machine gauge and the target fabric weight.
2. Fix the base yarn properties: count with system and ply, twist, strength and evenness.
3. Choose the functional route. Common options are cooling fibers and blends, profiled polyester for quick drying, acrylic, wool or heat-generating fibers for warmth, and fibers containing silver, copper or zinc for antibacterial use.
4. Test the function on finished fabric, after your finishing route and after washing.
5. Confirm the documents before bulk. For OEKO-TEX STANDARD 100, check the certificate number, holder, product class, scope and validity date; a logo alone does not show that the yarn offered is covered. For recycled content, ask for the GRS scope certificate and the transaction certificate for the shipment. Our article on OEKO-TEX certification in yarn quotes lists what to check.
6. Move from sample to pilot run to bulk, using the same spec and test plan at each stage.

Where Bulk Problems Usually Start

When a repeat order behaves differently from the approved sample, look at these causes first:

• An old test report. A report on an earlier lot only counts if the specimen, method and specification still match the yarn being shipped. Changes in fiber or processing may need new tests.
• Unclear count notation. “28S” or “1/28” without a count system, or a bulky yarn quoted at its as-spun count.
• A change of fiber source without notice. The count and blend are the same on paper, but the hand and evenness of the fabric change.
• Testing greige yarn only. Strength, shade and function are approved before finishing and then fail after it.
• Quotes compared on different bases. If two mills quote yarn specifications with different count systems, plies, spinning methods or functional components, the prices cannot be compared.

Two controls help a lot. The first is a lot number on every carton and cone, with retained samples for each lot. The second is lot test data (or a certificate of analysis) for the lot actually shipped. When you send an RFQ to VI-TEX, we can send the technical data sheet for the exact item and shade you plan to order.

Copy-Paste RFQ Checklist

Send the same list to every supplier, so the yarn specifications you get back can be compared line by line.

• End product and machine: socks, base layer, knit top, seamless or other; machine type and gauge; target fabric weight.
• Fiber content: generic fiber names and percentages, trade names next to their generic names, blend tolerance.
• Count: value, count system (Ne, Nm, tex or denier) and ply; single or resultant; for bulky yarn, before or after bulking.
• Spinning method and construction: ring, compact, siro, open-end or vortex; combed or carded; core-spun, covered or slub if relevant.
• Twist: tpm or tpi, S or Z, tolerance and test method.
• Physical targets: minimum tenacity (cN/tex), elongation at break, evenness CV%, IPI and hairiness, each with its test method.
• Function and evidence: the claim, the fabric test method and the number of washes.
• Color: color references, dye state, colorfastness tests and minimum grades.
• Dyeing and finishing route: dye class and pH, maximum temperature, heat-setting conditions, finishes.
• Documents: technical data sheet, lot test data, OEKO-TEX or GRS certificates that cover this yarn, and any other market requirements.
• Commercial terms: quantity per color, package type and weight, delivery schedule, Incoterms and destination.
• Order plan: sample, pilot run and bulk, with your lot-to-lot consistency requirement.

Send the completed checklist through the form below, or attach your current spec sheet. We will confirm the specification with you and send the technical data sheet for each proposed yarn.

FAQ: Yarn Specifications for Bulk Buyers

Which yarn specifications must we include in a bulk RFQ?

Include fiber content with generic names and percentages, count with its system and ply, spinning method, twist, and any special construction or functional component. Add color references and fastness requirements, quantity per color, package type and weight, required tests and certificates, delivery schedule, Incoterms and destination.

What test methods and acceptance criteria should a yarn purchase specification include?

Name a method for each property you want to control, such as ISO 2062 for tenacity and elongation or ISO 105-C06 for colorfastness to washing. A method only describes how a property is measured, so add the target or acceptance limit agreed with your buyer for the end use. Do not assume a universal pass grade from a method title or a product name.

Which yarn properties affect knitting efficiency the most?

Tenacity, elongation and their variation, plus thin places in the evenness test. These show up as end breaks and machine stops. A yarn with stable minimum values usually runs better than one with a higher average and a wide spread. Hairiness matters too, because it adds fly and fuzz on the machine.

How can we reduce shade variation and finishing surprises?

Put your dyeing and finishing route in the RFQ, agree colorfastness tests and minimum grades, and approve shade and strength on fabric that has been through the full route. For repeat orders, keep the fiber source, count and twist fixed, because a change in any of them can affect dye uptake.

Does controlling yarn properties reduce total cost?

The price per kilogram is only part of the cost. Machine stops, second-quality fabric, re-dyeing and customer returns usually cost more, and most of them start with variation between lots. A spec with targets, test methods and acceptance rules lets you stop a bad lot before it reaches the knitting floor.