Selecting a Sewing Thread

Essential Properties of Sewing Threads

A sewing thread must have good sewability and be capable of properly joining the two materials together. After joining these materials together, the sewing thread must last for the life of the product that it is sewed in.

The sewing thread must be durable. Contrary to popular belief, strength alone is not the primary prerequisite for a good sewing thread. It helps to have adequate strength, but the following items are just as important:

  • Uniform Diameter
  • Surface Lubricity
  • Suppleness
  • Low elongation
  • Torque Free (Balanced Twist)
  • Low Linting Characteristic
  • Resistance to Needle Heat
  • Free of Knots, Variation of Twist or Broken Pieces

Uniform diameter means no variation in thickness. This is important in modern high-speed machine sewing where thread tension is adjusted by passing the sewing thread between spring-loaded discs. A change in the thread diameter tends to increase or decrease the tension settings, resulting in unbalanced stitches and breaks.

Surface lubricity is the amount of frictional resistance offered by the surface of the sewing thread. The lower the resistance, the easier it is for the thread to pass through tension discs, guides, and the needle eye, making for a more uniform stitch.

Suppleness is the measure of the ease with which a loop is formed and is essential for a machine formed stitch. Generally, sewing threads of very high strength are stiffer and therefore are more difficult in getting consistently good stitches.

Low Elongation – the configuration of the sewing thread through the machine guides creates a certain amount of stress, which can result in thread elongation. The needle has to rise sufficiently to relax the thread before a loop can start to form. The lower the elongation, the less critical is the timing. This results in a wider range of tension adjustments and better stitch control.

Torque Free Strand is a sewing thread with proper twist balance to minimize kinking, tangling and missed stitches.

Lint Free – lint causes sewing thread breaks and unbalanced stitches when it collects in the tension guides and in the bobbin case. Lint, in the form of nep, also collects on the input side of the needle eye causing thread breakage.

Heat Resistance is the ability of the sewing thread to generate little heat due to friction with the needle and to withstand heat generated by friction between the needle and the fabric.

A sewing thread free of knots, variations in twist, and broken pieces gives higher machine and labour productivity, fewer rejects, and therefore lower stitching costs.

Durability Factors

The second requirement for good sewing thread properties and performance is its durability. The following factor contribute to good durability:

  • Seam Strength (loop strength)
  • Abrasion Resistance
  • High Elasticity
  • Shrink Resistance
  • Minimum Diameter
  • Colourfastness

Strength – where seams are involved, the most meaningful measure of strength is called the loop strength. This is the strength exhibited when one length of the sewing thread is looped through another and the loops are stressed. Straight pull strength is what is called single end strength, and is not a good measure of loop strength.

Abrasion Resistance means the sewing thread in seams resists wear during the life of the product. There are two ways abrasion occurs in a seam. These are the thread on thread abrasion in the stitch and the surface abrasion due to wear and rubbing.

High Elasticity is important because it helps determine the degree of stress or strength a seam can be subjected to without rupture. For instance when a fertilizer bag drops, very high stress (though momentary) is put on the fabric and the seam. The elasticity of the sewing thread absorbs this energy and prevents both the fabric from tearing and the stitch from rupturing. This elasticity is also necessary to maintain original seam appearance.

Shrink Resistance means a sewing thread must remain stable on drying after wash. It should not shrink at use temperature to prevent the article from developing pucker.

Minimum Diameter means that the sewing thread thickness must be appropriate for the thickness of the materials being stitched so that the thread should tend to bury itself in the fabric. This will minimize any damage due to surface abrasion during use.

Colourfastness is the ability of a sewing thread to retain its original shade of colour during washing and use.

Duralene Industrial Sewing Thread Characteristics

Theoretically, if one combined the factors that give good durability with those that give good sewability, then one would have the best sewing thread for the job. However, no single sewing thread can have all the good points mentioned above. One has to decide which of the properties are more important for a particular application. Most of the sewing thread properties can only be maximized at the cost of reducing some other equally important property.

All sewing threads exhibit the above-mentioned properties to some degree, but one must consider the following general statements: Cotton threads have very good sewability but are the least durable. Synthetics are harder to sew but are the most durable. While making Duralene® Industrial Sewing Thread, a good balance of properties has been chosen to obtain the best sewing thread for stitching of fertilizer and chemical bags, travel luggage, industrial filter cloths, tents and tarpaulins, etc. Duralene Industrial Sewing Thread is based on polyolefin multifilament yarn. Apart from having a good balance of all the above-mentioned physical properties, it has many other special characteristics:

  • Lubricity
  • Water Repellency
  • Chemical and Acid Resistance
  • Ultraviolet Resistance
  • Low Static Electricity
  • Mildew and Rot Resistant
  • Tensile Strength
  • Twist and Ply
  • Open Wind
  • Stabilization

Lubricity – Duralene Sewing Thread has been applied with a lubricant finish to control lubricity and improve sewability.

Water Repellency – Duralene Sewing Thread does not absorb water. If wetted, the water remains on the surface and therefore dries quickly.

Chemical and Acid Resistance – Duralene Sewing Thread is highly resistant to most chemicals and acids. Please ask for a detailed listing of its resistance to common chemicals.

Ultraviolet Resistance – all threads, synthetics as well as natural, degrade when exposed to ultraviolet rays in open sunlight. Duralene Sewing Thread has a UV retardant added to it so as to enhance its life. In the case of fertilizer bags the Duralene Sewing Thread stitching will last as long or longer than the bags themselves if the bags need to be stored in the open.

Low Static Electricity – Duralene Sewing Thread generates very low static electricity that helps in good unwinding from the bobbin and trouble free passage through the guides. Low static also helps reduce fire hazards in bags used for packing inflammable chemicals.

Mildew and Rot Resistance – Duralene Sewing Thread is completely resistant to mildew, fungus and bacteria, and will not rot even in wet conditions.

Tensile Strength – Duralene Sewing Thread has sufficient tensile strength to adequately meet the applications it has been design to be used in. Very high tensile strength is usually achieved at the cost of lower elasticity. Duralene Sewing Thread achieves a good balance between the two.

Twist and Ply – Duralene Sewing Thread is a three-ply yarn of primary (S) twist and secondary (Z) twist. The twist is based on the requirements of bag closing and other standard industrial sewing machines, rotation of the sewing hook, and the location of the looper. Only a few specialized machines, like the flatlock or the buttonhole, need a (S) twist (which can be supplied on order).

A right twist is called (S) and a left twist (Z). Holding a piece of thread vertically, the direction of the downward diagonal will be in the same direction of the diagonal of the letter (S) or the letter (Z).

Open Wind – Duralene Sewing Thread is wound on a tapered cone having a ribbon wind where alternate layers are wound in the opposite directions like the figure eight (8). This gives a much-improved take off compared to parallel of random wind. To further improve take off, open wind is used which has a wider spacing between alternate layers.

Stabilization – Duralene Sewing Thread is given a finishing treatment designed to reduce elongation, provide for immediate recovery after elongation, reduce shrinkage, and generally relax the fibers. This treatment is an absolute must for synthetic sewing threads.

Colourfastness – for applications requiring coloured sewing thread like in the stitching of travel luggage, Duralene Sewing Thread is solution or melt dyed. This gives excellent colourfastness, freedom from bleeding and migration.

Sewing Thread Selection: Cotton or Synthetic?

In selecting the proper type of sewing thread for any application remember this fact:

Cost of Sewing Thread = Purchase Price
+ Cost of Sewing (machine & labour efficiency)
+ Cost of Rejects (sewability)
+ Cost of Returns (durability)

Normally cotton will out-sew most synthetics due to its low elongation, suppleness, and heat resistance (ignoring its tendency to form lint and its accompanying problems). Synthetics are more durable due to higher elasticity and tenacity coupled with better abrasion and chemical resistance.

If low yarn cost is highly important and seam durability is of minor importance, one should choose cotton. If, however, durability is a major consideration, one should choose a synthetic.

Sewing Thread Terms

In addition to the many properties and terms mentioned above, there are several other sewing thread terms one needs to know about. For some end uses, e.g. polypropylene (PP) woven bags for fertilizers, one wants a sewing thread that will stretch, or elongate. By stretching or elongation the sewing thread until it breaks, one can determine how far it will stretch until it ruptures. A ten-inch length of thread may elongate to twelve inches before breaking; therefore 12” minus 10” divided by 10” gives us a 20% elongation at break. Cotton normally has 7% elongation, spun polyester around 15%, and Duralene filament sewing thread 20% elongation.

While elongation is important, more important is the ability of a thread to return to its original length after being stretched to near its breaking point. Duralene being a filament sewing thread has excellent recovery. Sewing threads made from spun fibres have less recovery and those made from cotton have the least recovery.

There is often some confusion between the “yarn count” used in weaving and the “ticket number” of common sewing thread. In the weaving industry when one speaks of #1 yarn count, it is 1 hank of 840 yards and weighting 1 pound. This is an expression of linear yield per pound. In other words, a numbering system based on length per pound.

In the case of sewing thread the “ticket number” is only indirectly connected with the length per pound. Here one is measuring the diameter of the thread in order to be able to use any ticket number, regardless of the plies or the length or weight, in the same needle size. For example all #70 threads should fit the same needle size. The 70/2 thread is made 40/2 yarn count which is equivalent to 20/1. The 70/3 thread is made from 60/3 yarn count, which is also equivalent to a 20/1. Theoretically, all #70 threads should fit the same needle eye.

Synthetic filament sewing threads are numbered quite differently. You take the total denier in the thread and add 10% of this total to account for contraction of the yarn when it is twisted. You then drop the last digit to get the thread ticket number.

Example 1 – (Duralene Filament Sewing Thread #115):
3 ends of 350 denier are twisted together 3 × 350 = 1050 denier
Add 10 percent (= +105)
Total: 1155 denier
Drop the last digit and you get thread ticket number #115

Example 2 – (Duralene Filament Sewing Thread #165):
3 ends of 500 denier are twisted together 3 × 500 = 1500 denier
Add 10 percent (= +150)
Total: 1650 denier
Drop the last digit and you get thread ticket number #165

For a particular sewing thread a convenient way of selecting proper needle size is to take a two foot piece of thread and see if the needle will slip easily from one end to the other as the opposite ends are alternately raised or lowered. If the needle does not slip easily from one end to the other by its own weight, the next larger needle should be tried.

Problems with Sewing Threads, and Their Causes

It is well known that to be able to make a quality product, a quality yarn is an absolute must – the best sewing machine with the best-trained labour cannot alone produce a well-stitched product if the thread is also not the best. The cost of the sewing thread is usually less then 5% the cost of the stitched product – a cheap poor quality thread can ruin a much more expensive completed product.

Some of the most common problems are:

Lost Ply – In a three-ply yarn, one end breaks back and allows the yarn to continue being twisted with only two plies running. If the operator puts this end back up without pulling off the entire length of the lost ply, one has a much weaker thread for the length of the missing ply.

Ply Knot – When a plied thread breaks and is tied back together, the large knot thus formed has difficulty being pulled through the needle eye. Knots are also a weak point in the thread and are prone to break easily.

Slubs – If a large group of fibres in a disarrayed condition enter a drafting system, they are only partially drafted out causing a larger torpedo shaped thick place in the yarn. In sewing threads this slub will cause sewing problems if it is large enough. If it is small enough to pass through the needle eye, it will spoil the finish of the seam.

Neps or Fuzz Balls – On the surface of the thread one can sometime see small bits or balls or lint or fuzz that are attached to the body of the thread in processing, immature fibres in cotton or curled up fibres in synthetics, abrasion of the thread during twisting and winding etc. This fuzzy material will sometimes gather in the tension guides or accumulate around presser foot or the needle eye to cause sewing problems.

Whipped Yarn – When the thread is being twisted, one thread may break and hit against the piece of metal that separates it from the adjacent thread being twisted. This causes the thread to fray and send small pieces of cotton or synthetic fibres into the path of the adjoining thread. Such damaged thread will make an ugly seam.

Under Wound – Thread is wound over or under itself due to improperly set winding machinery. This causes the thread to pull off cones or spools unevenly and can result in uneven tensioned stitches of thread breakage.

Wind too Close – Thread will not pull off smoothly, causing thread tension to vary.

Wind too Tight – Tend to over stretch the thread, in which case thread tends to spring open or get elongated. In extreme cases the cone may get crushed, wasting much of the thread.

Slipped Thread – In a poorly wound cone, the thread is not secure on the cone. Too loose a winding may make it unusable.

Slack Twist – Insufficient twist in thread lowers the tensile strength, and if too little, yarn sewability is reduced.

Corkscrew Twist – Uneven tension in the twisting process produces a corkscrew effect on the surface of the yarn.

Poor Balance – A condition in which the twists of the individual plies do not balance correctly with the twist of the combined plies. Unbalanced yarn, if held loosely, tends to twist on to itself. This hinders in the loop formation on sewing machines.

Dirty Thread – Grease of dirt in the thread during processing.

Uneven Lubricity – Unevenly applied lubrication finish on the yarn causes erratic sewing performance.

Crocking, Bleeding & Streaking – These are due to excess of dye in the thread, insufficient colourfastness, and uneven dying.

As can be seen, a lot of factors go into the making of good quality sewing yarn and in selecting one to suit one particular application. Please consider the materials written here carefully before selecting the type of sewing yarn for your particular application.