What Is a Yarn?

A yarn is a continuous strand of textile fibers or filaments suitable for knitting, weaving, braiding, or sewing. Yarns vary in:

• Fiber origin (natural, synthetic, regenerated)

• Structure (spun, filament, textured, fancy)

• Twist level

• Count/denier

• Surface characteristics

These factors govern whether a yarn needs sizing before entering the weaving process.

What Are the Different Types of Yarns Produced?

Yarns are broadly classified into the following categories:

1. Spun Yarns (Staple Fiber Yarns)

Made from short fibers twisted together.
Examples: cotton, viscose, wool, polyester staple, acrylic.

2. Filament Yarns

Continuous strands—either mono or multi-filament.
Examples: polyester filament, nylon filament, silk.

3. Textured Yarns

Filament yarns given crimp/bulk for stretch or softness.
Examples: textured polyester, air-jet textured yarns.

4. Fancy Yarns

Slub, boucle, chenille, neppy yarns—decorative structures.

5. Technical/Industrial Yarns

Glass fiber, aramid (Kevlar/Nomex), carbon fiber, polypropylene industrial yarns.

Each yarn type interacts differently with loom stress, influencing the need for sizing.

To learn more about the different types of yarns, click here.

Why Is Sizing Important in Weaving?

Sizing improves warp yarn performance by:

• Increasing tensile strength

• Reducing hairiness and dust

• Lowering abrasion at heddles and reeds

• Minimizing end-breaks during shedding and beating-up

• Enhancing weaving efficiency

In woven production, especially on high-speed air-jet and rapier looms, warp yarns face intense mechanical stress. A uniform sizing film—such as those formed by Alpenol’s adhesive and flexible chemistries—helps yarns withstand these forces and run smoother throughout the beam.

To learn more about sizing, click here.

Which Yarns Require Sizing?

1. Yarns That Definitely Require Sizing (High Priority)

A. Cotton Spun Yarns

Reasons:

• High hairiness

• Medium strength

• High abrasion during weaving

Applications: denim, shirting, sheeting, towelling.

Why sizing is essential: Alpenol-type systems reduce hairiness and strengthen warp, improving loom efficiency.

B. Polyester–Cotton (PC) and Polyester–Viscose (PV) Blends

Reasons:

• Synthetic portion adds smoothness, but cotton/viscose still swells

• Blends show uneven wetting without sizing

Applications: shirting, suiting, industrial fabric.

C. Viscose & Modal Spun Yarns

Reasons:

• Weak when wet

• High swelling tendency

• High friction

Applications: dress materials, flowy fabrics, home textiles.

D. Woolen & Acrylic Spun Yarns (in weaving)

Reasons:

• Loose structure

• High bulk and fiber movement

Applications: blankets, upholstery fabrics.

2. Yarns That Sometimes Require Sizing (Conditional)

A. Filament Polyester (FDY/POY/DTY) for High-Speed Weaving

Reasons (conditional):

• Smooth surface usually sufficient

• But fine deniers (20D–75D) may break under tension

• High-speed air-jet weaving benefits from light sizing

Applications: sarees, curtains, lining fabrics, lightweight dress materials.

B. Filament Nylon

Rarely needed, except:

• Microfilament constructions

• High-drape fabrics requiring low-fuzz performance

C. Technical Textiles Yarns (glass, aramid, carbon)

Some require special-purpose sizing (not textile sizing), such as coupling agents or polymer coatings.

Applications:

• Composites

• Filtration

• Fire-resistant fabrics

3. Yarns That Usually Do NOT Require Sizing

A. Knitting Yarns

Knitted yarns are NOT sized.
Reasons:

• Knitting requires flexibility, not stiffness

• Sized yarn becomes too rigid

• No warp tension or reed abrasion in knitting

B. Most Filament Yarns

Examples:

• Polyester filament

• Nylon filament

• Silk

Reasons:

• Continuous, smooth

• High strength

• Low hairiness

• Good abrasion resistance

Why Do These Yarns Require Sizing?

Spun yarns have:

• Short fibers protruding (hairiness)

• Increased friction

• Lower tensile strength

• Greater abrasion susceptibility

Sizing compensates by:

• Binding protruding fibers

• Forming a protective film

• Increasing yarn stiffness to withstand loom dynamics

• Improving uniformity

Alpenol’s modern formulations create flexible, abrasion-resistant films that reduce brittle behavior and dusting, especially on cotton and viscose warps.

Why Do Some Yarns Need Sizing While Others Don’t?

Yarns That Need Sizing

• Warp yarns in weaving are most commonly sized because they undergo high tension and friction on the loom. Sizing helps prevent breakage and reduces fuzz, making the weaving process smoother.​

• Yarns with low twist, high hairiness, or made from delicate fibers (like silk or certain blends) often require sizing to maintain integrity and improve handling.​

• Filament yarns or elastic yarns may also be sized to control shrinkage and enhance dimensional stability.​

Yarns That Do Not Need Sizing

• Weft yarns in many cases do not need sizing because they experience less tension and abrasion during weaving.​

• High-twist, smooth, or tightly spun yarns are generally strong enough to withstand processing without additional coating.​

• Yarns used for knitting or crafts (rather than industrial weaving) often do not require sizing, as their end use does not subject them to the same stresses.​

Factors Influencing Sizing Need

• Fiber type (cotton, wool, synthetic, blends)

• Twist level (higher twist yarns are less likely to need sizing)

• Yarn structure (filament vs. staple, singles vs. plied)

• End application (industrial weaving vs. handcrafts)

How Does Sizing Improve Weaving Performance and Final Fabric Quality?

1. Reduces Warp Breakages

Major cause of loom downtime.

2. Improves Abrasion Resistance

Yarn withstands healds, reeds, and temples better.

3. Enhances Smoothness of Fabric

Less hairiness = cleaner surface = better appearance.

4. Improves Efficiency and Lower Production Costs

More picks per minute with fewer stoppages.

Sizing’s contribution is especially visible in critical warp-dominant fabrics like denim, poplin, shirting, and technical wovens.

What Are Common Sizing Agents for Cotton, Polyester & Blends?

Alpenol's balanced, modern systems minimize add-on requirements and reduce viscosity drift—ensuring predictable warp behavior shift after shift.

When Is Sizing Necessary for Spun Yarns vs Filament Yarns?

Spun Yarns → ALWAYS for weaving

Cotton, viscose, wool, acrylic, PC, PV blends.

Filament Yarns → SOMETIMES

Microfilament polyester, nylon, and very fine deniers used in high-speed weaving.

To learn more about spun yarns and filament yarns, click here.

Sizing Requirements for Warp Yarns Compared to Weft Yarns

Warp Yarns → Require Sizing

Because they undergo:

• Shedding

• Tension

• Abrasion

• Beating-up

Weft Yarns → Rarely Sized

Reasons:

• Minimal tension

• Not subject to the heald or reed movement

This is why warp beams are prepared with sizing, while weft yarns usually remain untreated.

Do Yarns Used in Technical Textiles Require Sizing?

YES — IF woven with high stress

Examples:

• Industrial polyester

• Polypropylene tape yarns

• Glass fiber weaving

NO — IF already coated or part of a composite

Aramids, carbon fibers, basalt fibers may use specialized coupling agents instead of textile size.

Sized vs Unsized Yarn: Performance Differences

Sizing gives the warp yarn structure and stability to handle demanding high-speed weaving operations.

FAQ

1. Which yarns require sizing?

Mainly spun yarns: cotton, viscose, PC/PV blends, wool blends, staple polyester.

2. Do filament yarns need sizing?

Not usually—only for fine deniers or technical weaving.

3. Are knitting yarns sized?

No, because sizing reduces flexibility and knitting involves low tension.

4. Why do spun yarns need sizing?

To reduce hairiness, improve strength, and reduce abrasion during weaving.

5. Does sizing improve fabric quality?

Yes—smoother surface, fewer defects, and stronger fabrics.

External References

1. Textile School – Yarn classification
   https://www.textileschool.com/articles/yarn-types/

2. Textile Learner – Sizing and weaving preparation
   https://textilelearner.net/category/weaving/

3. ScienceDirect – Yarn mechanics & sizing behavior
   https://www.sciencedirect.com/topics/engineering/sizing

4. NPTEL – Yarn manufacturing & sizing technology
   https://nptel.ac.in/courses/116/102

5. Fibre2Fashion – Articles on yarn performance & sizing needs
   https://www.fibre2fashion.com/industry-article/yarn

Indian Textile Journal – Weaving preparation & warp protectionhttps://indiantextilejournal.com