Sewing Thread

Sewing threads are special kind of yarns that are engineered and designed to pass-through a sewing machine at high speed while forming a stitch. “There is no perfect thread for all applications, however there is a perfect thread for the specific application” (A & E).

1. Functions of sewing thread
Threads are expected to maintain two functions aesthetics and performance for stitching and seams during the life of the products

I. Aesthetics: color, luster, and fineness are primary selection factors when thread is used for decorative purposes such as top stitch or embroidery. Other aesthetics consideration includes hue and shade matching and colorfastness of thread.

II. Performance: Thread performance is related to sewability and seam performance. Sewability of thread is dependent on consistent loop formation and resistance to breakage.   Seam performance is related to loop formation, seam strength, abrasion resistance, elasticity, chemical resistance, flammability, and color fastness. 

Thread used in garments must be durable enough to withstand the abrasion and needle heat that occur with high-speed sewing, the chemical forces garment finish and care, and stretch and recovery during wear.  

Sewability parameters  
The parameters that define the superior sewability of thread are;

• No breakages in high-speed sewing
• Consistent stitch formation
• No skipped stitches
• Evenness, to prevent changes in tension during sewing
• A high level of abrasion resistance
• Sufficient surface smoothness, to pass easily through the machine guides.                         

2. Characteristics

Threads have many different characteristics, and appropriate selection is dependent on knowing the properties required. Factors that contributes to the esthetics and performance of sewing thread include fiber content, structure, twist, ply, color, finishes, strength, size, and put-up. 

I. Fiber content: fibers most commonly used are cotton, polyester, nylon, and rayon. Each fiber has its own properties and particular fiber is chosen for particular application to deliver the right results.

Cotton: Cotton threads provide the standard for sewability of stitches and appearance of seam. It has excellent sewability because of its flexibility loop-formingability.

Rayon: Rayon has the absorbency and flexibility of cotton and the luster of the silk and it is not as susceptible to the needle heat problems of thermoplastic threads, but it has low elasticity and strength when wet.

Polyester: Polyester thread is considered a general purpose thread because of its versatility. It is high in tenacity and abrasion resistance.

Nylon: Nylon thread is soft, fine, and high in tenacity and abrasionresistance.

Specialty: Some tread are produced from specialty fiber to meet the specific performance needs. Such as Aramid, Metalic, Elastic 

Comparison of different sewing thread properties
Properties	Cotton	Polyester	Nylon
Strength	Low strength	High strength	High strength
Elongation	Low elongation	High elongation	High elongation
Abrasion Resistance	Not as good abrasion resistance as  synthetics	Not as good abrasion resistance as nylon	Excellent abrasion resistance
Color fastness	Color fastness not as good as polyester	Very good color fastness	Color fastness not as good as polyester
Chemical resistance	Not as resistance to chemical as synthetics	Excellent chemical resistance	Good chemical resistance

II. Thread structure :

Thread structure has significant role or effects to thread functions. The types of yarn structures used in producing sewing thread are spun, filament, core spun and air- entangled. 

a. Spun yarn: Spun yarns are made from staple fibers that are aligned and twisted together to form simple, single yarn. Singles are twisted again together to form multiple-ply sewing thread. The number of ply may vary from two to nine. Spun yarns are made of cotton fibers and or polyester staple fiber. Spun polyester (S/P) thread is considered a general purpose thread. It is one of the more widely used thread and least expensive. 

b. Filament: Filament threads are stronger than spun thread of the same fiber and size made. Three types of filament threads are commonly used.

• Mono filament is produced from a single continuous filament fiber with a specific thickness. It is strong and uniform, so breakage during sewing is minimal, and it relatively less expensive. For lack flexibility and other limitations monofilament thread are used for hems in budget garments and for seam and hems in draperies and upholstered furniture. 
• Smooth multi filament threads are usually made from nylon or polyester and are used where high strength is a primary requirement. Smooth filament thread may be single continuous filaments or multiple continuous filaments that are twisted or bonded together. 
• Textured filament threads are produced from polyester or nylon continuous filament fibers that are textured and heat set to ensure bulk retention. Textured filament is used primarily as the looper thread for cover and overedge stitches. Texturing the filament fibers gives thread more cover and elasticity but reduce luster and makes the thread more subject to snagging during sewing and use.

C. Core spun thread is a combination of staple and filament fibers. The most commonly used core spun thread has multiple-ply construction; each ply consists of a polyester filament core wrapped with either polyester (poly wrapped poly core) or cotton fiber (cotton wrapped poly core). Core spun thread is higher in tenacity and cost more than S/P thread.

d. Air-entangled thread is a fairly recent development in texturing polyester with no twist. Continuous filaments of polyester are entangled as they pass through a high-pressure air jet.

III. Twist

Twist refers to the turn per unit length of thread and is required essentially to hold the fiber/ply together to give the yarn /thread substance the required strength and flexibility. If twist is too low thread may fray and break. If twist is too high, thread become “lively” which result in looping or knots that prohibit stitch formation.

The direction of twist is identified as Z for left twist and S for right twist. Most sewing threads are made with Z twist because of sewing machine are designed. S twist thread is better for flat lock or cover stitch machine. 

IV. Ply 

Single stand of yarn are plied or twisted together to form a yarn or thread. Plying increases durability and performance. Most all spun and core spun threads are produced in two or three-ply to provide greater strength. Two-ply threads may be sued for fine delicate fabrics. Three ply threads provide greater strength for seams; four-ply thread may be used for more durable construction. 

V. Color

Two aspects of color are important for esthetics and performance of threads: color matching and color fastness.

• Color matching of threads and piece goods is essential when seam are to be inconspicuous. The color match between a thread and particular piece goods may depend on the dyestuff selection, and dye-ability of the fibers in the thread. Success of visually matching colors depends on the type of light, nature of the surrounding, and the viewer’s ability to see color difference.
• Colorfastness generally means fastness to light and washing, although threads may be subject to other color-altering conditions such as abrasion, chemicals, dry cleaning, and pressing. 

VI. Finish

Finishes on sewing threads are used to increase sewability by increasing strength and abrasion resistance, bonding fiber together, or lubricating the thread.

• Soft cotton thread: no farther processing to change its physical characteristics. It is only dyed and lubricated. 
• Mercerized: In this process cotton thread is treated in a caustic solution under controlled tension. This causes the fibers to swell, resulting in a greater affinity for dying. Mercerization also increases the luster and ads some strength. 
• Gazed: Passing cotton thread through a flame at high speed to reduce the fuzz is known as gazing. This process also produces a higher sheen. 
• Glazed: This is a process in which cotton threads are treated with starches and special chemicals under controlled heat and then polished to a high luster. The glazed process results in a thread with a hard finish that protects the thread from abrasion and enhances ply security. 
• Bonded:  Treating continuous filament nylon or polyester with a special resin that forms a protective coating on the surface called bonding.  It increases thread’s smoothness, ability to resist abrasion and greatly enhances ply security. 
• Lubrication: Thread lubrication has two purposes to reduce the amount of friction and to provide protection from needle heat. The lubricant must also be non-staining, non-soiling and must have negligible effect on thread color.

Similarly there if other finishes such as non wick, anti fungal, fire retardant, water repellent, anti static etc. to suit a particular functional requirement.

VII. Strength: 
Tensile strength measures in gram or kilograms the breaking point of a stand of thread under tension. Thread strength is related to size, fiber content, amount of twist, number of plies, finish. Thread must be strong enough to withstand the friction of stitching and to hold the garment piece together during wear and care.

VIII. Thread size: 
Thread size refers to the diameter or thickness of the thread. Thread is indicated by ticket number, denier, and cotton count. Thread should be as fine as possible depending on the required strength of seam.

Fabric Weight and Typical Thread Sizes

Fabric	Oz./Sq.Yd	Grams per  Sq Mtr.	Thread Tex Sizes	English Cotton Count
Ex-Light	2 – 4 oz.	68 – 136gr.	16, 18, 21, 24	50/2
Light	4 – 6 oz.	136 – 204gr.	24, 27, 30	40/2
Medium	6 – 8 oz	204 – 272gr.	30, 35, 40	40/2, 40/3
Med. Heavy	8 – 10 oz.	272 – 339gr.	40, 45, 50, 60	20/2
Heavy	10 – 12 oz	339 – 407gr.	60, 80, 90, 105	20/2, 20/3
Ex-Heavy	12 – 14oz	407 – 475gr.	105, 120, 135	20/3, 20/4

Cotton count = 590.54/Tex

IX. Thread package : 

Sewing thread are put-up on different types of thread package called spool, cops or tube, cone, king tube or vicone, containers, cocoons, and rewound bobbin to suit different types of threads, machine, and sewing needs. Thread is sold by length instead of weight.

3. Alternatives to sewing thread

Adhesive and laser-enhanced bondings are alternative to sewing thread for seaming and garment assembly. Use of adhesive in place of thread on textile material has limited success because the peel strength on textile is low. Peel strength is the primary measure of adhesive strength. Protected tape may be bonded over seam to make seam waterproof. Welding technique relay on thermoplasticity of synthetic textile materials. Layers of material are melted, fused, and cooled, creating a bond. Another system of bonding is ultrasonic welding “The technology entails utilization high frequency vibration to bond together two or more material. The vibration generates a rapid buildup of heat within the material which causes the materials to melt and fuse”.