Thread Science
Thread Construction Types
Needle Selection
Seam Properties
Common Sewing Solutions

Thread Science:


Have you ever wondered how long sewing threads have been around?

The answer is almost as long as humans have walked on two legs. The first threads would have been little more than thin leather, animal tendons, sinew or twine. Many ancient tribes knew which local plant or tree gave the best thread such as honeysuckle, reed and cactus. In Europe clematis or Old Man's Beard was used for millennia as twine, it has amazing strength.
In 1793 Mrs. Samuel Slater (Hannah Wilkinson) from Rhode Island was awarded a patent for a cotton sewing thread which she had twisted on her spinning wheel though Cotton was first spun on machinery in England in 1730.  Two and half centuries later, Mr. Walter Wayne Freed registered patent (US3626441) for Polyester Sewing Thread at 1969.

Fibers come from two different sources.

Natural fiber: These fibers are generated from natural sources like plant or animal. Cotton is predominantly the most popular and common natural fiber used to make thread. Other natural fibers include rayon, Lyocel, silk, wool, jute, Abaca, Coir, Flax, ramie, hemp, and linen. Modern researchers have come up with various others sources like spider silk, sisal, Alpaca etc.

Synthetic Fiber: Various chemical substances and multi-step process produces synthetic fibers. Common synthetic fibers are Polyester and Nylon. Other specialty syntheticfibers include polypropylene, aramids including Kevlar®, Technora, Twaron & Nomex®, PPS, and PTFE. Regeneration of various natural fibers has also stepped up to fill other voids.


Thread Dyeing

Threads are dyed in package dye machines in different bulk sizes under required pressure and temperature. Different dye types and temperatures are used to achieve the desired shade and color fastness requirements for different fibers depending on requirement. Natural Fibers like cotton fibers are dyed in disperse dyeing process whereas Synthetic fibers such as Polyester and Nylon are dyed using Reactive processes. In Eco, we use all eco-friendly and ZDHC certified dies and chemicals for dyeing purpose.

Another important measure of thread production is lubrication under finishing section. lubrication is the process of putting on the thread prior to winding for protecting the thread against needle heat and enhancing sew-ability and lubricity characteristics during functioning through the sewing machines.


Thread Construction Methods:

Spun thread

Cotton or polyester staple fibers are spun into single yarns and then twisted together. We have 2 types of Spun thread in Eco.
Spun Polyester: Ecospun and Spun Cotton: Ecocot

Spun cotton or polyester staple fibers are wrapped around filament polyester
fibers. Our Product range involves:
Cotton Wrap Polyester Core (PCC): Ecocore
Polyester Wrap Polyester Core (PPC): Ecopoly

Core-spun thread
Textured thread

Texturing is a mechanical procedure used to increase the volume and the elasticity of a Polyester or Nylon filament yarn to make the thread fuzzy and stretchy. The essential properties of textured yarns and the products made from them are softness, fullness, a high degree of elasticity, thermal insulation and moisture-transporting properties. We offer textured polyester thread in the name of Ecotex.

Filament threads are made from Continuous, long, thin strands of Polyester or Nylon fibers that are twisted together to form a shinier product. filament polyester threads have excellent elongation (the fibers can stretch and recover), smooth presence with no lint and can be finished as “thick or thin threads”. Eco thread offers a unique thread named “Ecofil” of this type of construction.

Filament thread
Mono-filament thread

Monofilament threads are a single strand of polyester or Nylon fiber, similar to fishing line. It's usually a very fine thread blends very well and can be ironed on medium heat.

A strength-enhancing resin is coated on the outside of the thread. This increases the tensile strength and helps reduce friction. Bonded threads are usually meant for upholstery and heavy-duty sewing applications.

Bonded thread

Needle Selection:

*This table is for reference purpose only
Fabric Type Fabric Weight/Density Recommended Needle Size Needle Point Recommendations
American European
Knitwear Light 9-10 65-70 Light Ball Point, Slim Point
Medium 10-11 70-75
Heavy 11-12 75-80
Woven Fabric Light 8-9 60-65 Regular Point, Slim Sharp Point
Medium 9-10 65-70
Heavy 10-12 70-80
Denim Medium 11-12 75-80 Regular Point, Slim point
Heavy 12-14 80-90
Extra Heavy 14-16 90-100

SPI Recommendation:

*This table is for reference purpose only
Fabric Type Garment Recommended SPI
Lock Stitch/Chain Stitch Overlock
Knit Sweaters 8-10  
  T-Shirt, Kids-wear, Fleece, Female wear 10-12 12-14
  Underwear, Swimwear, Intimates 10-12 12-16
  Stretchable knits 12-14 14-18
Woven Kids-wear, Twill Pants 8-10 10-14
  Dress Pant, Skirt, Trousers 10-12 12-14
  Dress Shirt, Fine Blouse, 12-18 12-18
  Blindstitch 4-6  
Denim All Denimwear 7-9 10-12
Special Notes:
  • More SPI with Finer thread sizes helps minimizing Puckering
  • More SPI provides better seam Coverage during Serging operation and Fleece.
  • SPI should increase with higher seam elasticity to prevent stitch cracking
After wash process, Denims tends to show higher SPI than unwashed garment.

Seam Properties:

Seam is the combination of stitches which make line to join two or more “Ply” of fabric basically used as functional and decorative purposes. Seams are widely used in modern mass-produced apparel, footwear, house hold textiles and sporting goods which are sewn by different industrial sewing machines. Arrangement of fabric ends of the seam line is called seam type. There are eight classes of seam defined as per ISO 4916:1991.


Seam ClassSeam NameAssociated Stitch ClassesMost Common Usages
1Superimposed seam301, 401, 500 ClassesEdge Joining of Apparels
2Lapped seam401Denim, Overcoat, Twill
3Bound seams301, 401T-shirts,
4Flat seams304, 401, 602, 605, 607Lingerie, Fine Tailoring, Activewear, Swimwear

These 4 Stitch classes are more often practiced in apparel industry. Other Seam Classes involve Decorative stitching, Edge neatening, Attaching of separate items and Single ply construction. There are various types of seams (sub-classes) within this classes.

Important parameters of Effective Seam:

Seam Strength:

The main factors of the seam strength are seam type, the stitch type, stitch density, fabric strength, thread strength, and the tension of thread which is applied in the seam. A lapped seam is the strongest of all seams because the fabric is lapped upon itself and the sewing threads contribution is mainly to hold the lapped plies in place. The lockstitch is the most common stitch type in garments industries, but it is easily damaged. Chain stitch and over edge stitch types are higher seam strength and greater extensibility than a lockstitch. The number of stitches over a given length of seam that is called “stitch density” which is direct influence on seam strength. The seam needs to be engineered to deliver a balance between the stitching and the strength of the material being sewn. Thread tension is critical for the seam strength and seam elongation. If the thread is too tight in the seam its natural elongation is withdrawn allowing the thread to fail prematurely.

Determining seam strength:

The simple method of estimating seam strength based on two parameters.

Stitch Type

Lock Stitch

(Stitch Class – 301)

Chain Stitch

(Stitch Class - 401)

FormulaEstimated Seam strength = SPI x STS x 1.5Estimated Seam strength = SPI x STS x 1.7
ExampleStitch per inch (SPI) = 7
Single Thread strength (STS) = 1000 g
So, Seam strength = 7 x 1000 x 1.5 = 10500 g or 10.5 kg
Stitch per inch (SPI) = 8
Single thread strength (STS) = 1200 g
So, seam strength = 8 x 1200 x 1.7 = 16320 g or 16.32 kg


Seam Durability:

Durability of seam should be equal or higher than that of fabric. A seam must be durable, long lasting and not abrade (scrape) or wear easily during everyday use of the garment including all necessary laundering.

Seam Security:

Security is closely connected with durability. A seam needs to be secure and not to unravel or broke during everyday use of the garment.

Thread Size & Ratio:

Selecting the right thread for desired seam is the most important thing. Thread has to be selected considering Fabric properties and Washing process (if any). For example, If elasticity is expected from a seam, involving thread should have necessary elasticity. In modern denim industries, Various process such as scrubbing, Laser fading/burning and Wash have become popular. In order to achieve these results, thread has to be selected accordingly which can withstand these effects.

Thread sizes should be balanced when seam is to be formed. For example, In lockstitch, Needle thread should be higher in sizes with respect to bobbin thread. If not, seam will show deformity.

Another key fact of a fine seam is balanced thread ratio. For example, in Chainstitch – Ratio of Needle and Looper thread should be close around 60:40 (might vary to small extent depending on the fabric thickness). If this ratio is altered, formed seam will lose its shape and sharp edges might produce.

Common Sewing Solutions:

Skipped stitches:
Problems Recommended Solutions
Sewing Thread is Unable to form loop Thread needs to be changed.
Imbalanced thread tension on upper or lower loop. Tension of thread needs to be adjusted.
Needle deflection effect. Needle needs be changed.
If needle thread loop size is too small. Needle size and thread needs be checked.
Fabric flagging is noticed during sewing. Pressure foot pressure needs to be adjusted.
Failure of hook or looper and needle to enter loop at correct time. Examine the setting and timing between needle and hook or looper
    Imbalance stitch:
Problems Recommended Solutions
 Imbalanced tension of sewing thread Re-adjust accurate Thread tension
 Threading is not done by proper way Check all guide & Vain for thread path
Needle Snagging with Bobbin is observed Bobbin case to be smooth and reset
Sewing threads are not perfectly lubricated. Better quality threads needs to be used.
Staggered stitch:
Problems Recommended Solutions
Un-aligned Feed-dog motion Re-adjust Feed-dog motion
wrong needle point. Needle Needs to be changed.
Wrong Selection of needle and thread size. Needle size and thread size needs to selected accordingly.
Fabric does not perform smoothly in feed mechanism. Pressure Foot needs to be re-adjusted for perfect pressure.
Variable stitch density:
Problems Recommended Solutions
Improper winding and Twisting of Needle thread Thread needs to be changed, Thread package height needs to adjusted and check guides and vains.
Fraying, twisting of Needle thread at Guides Thread should be fine, correct threading is required
Sewing thread and Hook gets heated Proper Lubrication of thread and Hook positioning are needed
Excessive tension of thread. Tension of thread should be less or use of higher strength threads.
Spring damaged, non-flexible Tension post Spring needs to be changed.
Seam puckering:
Problems Recommended Solutions
Seam looks creepier and dense Thread Tension needs to be adjusted
Improper thread Tension Under Thread should be tension free
Imbalanced stitch ratio Stitch ratio has to be maintained accurately
Wrong Needle and Thread Size Finer sizes of thread and Needle is required
Seam Hairiness
Problems Recommended Solutions
Imbalanced Stitch ratio at Chainstitch and Overlock Stitch Ratio has to be maintained strictly
Thread Fibers attached at Needle guides and vains Needle guides and Vains should be edge free and smooth.
Thread contains fraying Good quality thread should be used
Needle thread breakage:
Problems Recommended Solutions
Low tensile strength of Thread Good quality thread is required
Excessive tension to the Needle and bobbin threads. Tension adjustment is needed
Bobbin case Edge, looper eye are sharp The edges should be smooth.
Incorrect fitting of bobbin case. Case size and fitting needs to be rechecked.
Knots, Naps and Thick-thin end present in Thread Thread should be uniform in cross-section
Thread Plies breakage when sewing machine stops:
Problems Recommended Solutions
Blunt thread cutter of Sewing Machine Needs to be replaced
Sudden pressure at thread during starting of sewing Timing needs to adjusted
Needle gets damaged after sewing thread breaks Needle should be changed.