Strong sewing thread- a heavy-duty yarn

This post is about sourcing strong sewing thread for economical sewing of strong and durable DIY adventure gear.

Introduction and background to my search for strong sewing thread

I have used strong sewing thread for over more than 50 years to make my own adventure gear using sewing. Judging by the number of 5,000m reels of thread that I have used over that time, I must have done more than10 km of stitching. “No, it wouldn’t reach the moon.” My last big commercial roll of thread was kindly given to me by someone who said it was too thick for her sewing machine, but for my projects it was just right. It was my preferred polyester thread with a breaking strain of about 1.5kg and with a suitably sized needle it flowed easily through my domestic Elna sewing machine.

As I watched my latest reel dwindle while making multiple down quilts, I realised that I would need to find a good source of heavy polyester sewing thread to continue my projects. I determined that the breaking strain of my current strong polyester thread was about 1.5kg and that I would settle for a breaking strain of approximately 1.0 to 1.5kg.

My primitive online searching failed to find a commercial/economical roll of strong sewing thread with a well-defined specifications that would clearly meet my unusual requirements. Online advertisements often lack tight specifications that allow the purchaser to know exactly what is being offered. The five rolls of inferior thread shown in the photo below are the result of such an ill-informed purchase. “Cheap but not as strong as I had hoped.”

Luckily, my IT-savvy daughter kindly came to my rescue. She decoded the cryptic thread specifications using AI. Then she performed targeted searches for threads from reputable makers. I thought that posting about our search results and the threads’ suitability might help others to confidently source threads for their gear projects. My choice was a Coats product, ‘Epic Thread 5000m Col 2700-TKt-80’ available online from Jack Stock Heberdashery. While this product ID may be all that you need, you may be interested in finding out more about my decision process.

Thread specification

The codes used to describe the threads can contain a lot of useful and sometimes confusing information. Knowing how to interpret the code is the key to success, particularly when they are from reliable brands such as Coats and Gutterman.

My main requirements were strength, durability, rot resistance, and machine-sewability. From years of experience, sewing threads spun from polyester have been an excellent choice for making durable DIY backpacking gear.

A thread breaking strength of ~1.5kg has been my target, and it is probably gross ‘overkill ‘. However, overkill in the sewing room is better than a risk of failure in the bush.

Multiple thread codes relate to thread strength, such as TEX and TKt (Ticket). To make things complex these common ones have an inverse relationship with each other. As thread strength goes up, Tex goes up, while TKt goes down.

TEX. This is the metric scientific measure of thread thickness and is the weight in grams of 1,000m of thread. It increases with thread thickness and thread strength with all other things being equal.

TKT or Ticket. TKT is a commercial label assigned to threads and will often be part of the product description. It is determined approximately as: TKt=3,000/TEX. Conversely, TEX=3,000/TKt

For example, for my chosen heaviest thread (Coats Epic Polyester Corespun TKt 080 TEX 040, 5000m reel) made from virgin polyester, the TEX can be estimated from the TKt (80): TEX=3,000/80=37.5. It has a breaking strain of ~2.0kg according to AI and 1.8kg by my primitive testing (described later).

Additionally, I purchased a lighter thread to experiment with. It is made from recycled polyester (Coats Epic ecoV 100%Recycled Polyester Corespun TKt 120 TEX 024, 5000m reel). Its TEX would be 3,000/120= 25. It would have a breaking strain of ~1.0kg according to AI and 1.4kg by my primitive testing (described later).

Both of these breaking strains met my desired requirement of a minimum of 1.0kg while the 2.0kg well exceeded the strength of my current source of sewing thread (est 1.5kg).

Corespun thread structure. This corespun term means that the thread is made with multiple twisted ply strands. Inside each ply strand are strong, smooth, and stiff filaments which are coated with softer fibres. This provides high strength while giving the thread good machining properties and a soft feel in the finished product (Coats Bulletin 07). “No doubt, the soft feel to our bodies is also is an indication that the thread is also gentle on the fabric and reduces the tendency to start tears under extreme loading.

Choice of thread fibre. My first big reel of strong thread was a polyester/cotton composite. It was suggested as being appropriate for sewing japara (cotton) tents and canvas backpacks in the days when synthetic fabrics were only becoming available for the military and those ‘in the know’.

Fortunately, my father did building work at a factory making early PU coated nylon fabric in dreary colours for the military. He procured some factory seconds for me to make tents and other backpacking gear with. The argument for using polyester/cotton composite thread then was that it was strong, largely rot-proof and the cotton component made it gentle on seams sewn in somewhat weaker cotton fabric. There was also talk of the cotton component swelling when wet and thereby making the stitches more watertight. I now doubt that any of this was true or important. I now consider that heavy (TKt 80) 100% corespun polyester thread is suitable for all my sewing needs, from heavy fabrics down to the lightest quilt materials.

Primitive strength testing. I tested the strength of the threads by suspending a two-litre milk bottle on the thread and loaded the bottle with water using increments of 100ml to reach the breaking point, as recorded below as the greatest weight (kg) that each thread supported:

Domestic sewing cotton 0.8

Cheap ill-defined polyester 0.9

Coats Epic ecoV 1.4

Coats Epic Polyester 1.8

Previous strong sewing thread 1.5

I was glad that I did the above testing, as I was quite surprised by the relative strength of the domestic and cheap threads……..

How do the threads perform on my sewing machine?

To test the sewing threads, I sewed a sample of my lay-flat seam that I use to make strong tent seams with embedded tie-out tabs. I use these strong four-layered seams to connect tie-out tabs within the seam layers. To prepare the tie-out tabs for easy sewing into the seam, I sew the two ‘legs’ of the tab to form a V-shape within a web of polyester fabric.

I used my previous strong polyester thread, Coats Epic Polyester and Coats Epic ecoV, to sew sections of the tent seam. This seam usually incorporates multiple tie-out tabs and the stitches that hold these tabs experience considerable loading in strong wind and snow loading. At the junction of the tie-out tabs ten layers of fabric were sewn through (4 for layers for the seam, 4 for the folded tie-out tab and two for the spreader web). Then for the span of the web, I backstitched twice (1 backwards and 1 forwards again to continue the normal stitch line). The three threads sewed easily during this sewing operation, including the backstitching. “The stitching is possibly a little ugly, but it makes a strong seam and an even stronger tie-out with insignificant bulk or weight.”

Discussion and conclusion

The strong sewing threads; Coats Epic Polyester and Coats Epic ecoV, both performed well and will be used for my ongoing sewing of adventure gear. Although probably not neccesary, I will use the Epic thread for tents and high-load situations and the Epic ecoV, for quilts and similar uses, where thread strength is less important. Both threads should be just as durable as my previous polyester thread.

Tim