What Is the Strongest Sewing Thread?


Whenever you sew for your business or personal use, you want to ensure you have the best thread for your items. You wouldn’t want your shirt unraveling from a poor choice in sewing thread, would you? Finding the strongest and appropriate thread for your projects can prevent a disaster.

The strongest sewing thread today is the Kevlar thread. Fire retardancy, ballistic resistance, and the ability to withstand heat up to 800°F (426°C) are the capabilities kevlar thread has. This thread is used by the military, first responders, and other consumers who need a heavy-duty product. 

Before you automatically buy the Kevlar thread, you should learn and compare it to other lines. I will tell you what strengths each thread has and what and how they are used. You will also find out later on what 40wt means and other sewing facts. 

What Is Kevlar Thread?

Kevlar thread is used in creating heavy-duty items, first responder equipment, and clothing. It is 2.5x stronger than nylon and polyester thread. 

Kevlar thread provides strength, durability and does not sacrifice comfort. Dupont is trusted by the U.S Military, firefighters, and even customers who use their products. 

With heat resistance and incredible tensile strength, Kevlar is stronger than steel and supports ballistic resistance. These are only a few advantages of this fantastic thread. But how does it fare compared to other threads?

Can Kevlar Thread Be Used for Sewing?

Anyone can use Kevlar thread for sewing. This thread is excellent for everyday items like cords, Goodyear tires, and some fantastic pet toys. There are no limitations on what this thread can create. 

What Is the Thickness of Kevlar Thread in a Sewing Machine?

The average thickness for Kevlar thread is 1.14mm (0.04 in). It can go up to a size 69 in personal sewing machines, making it perfect for at-home projects with ease. This thread can even be hand-sewn if you need more detailed stitching. 

Sewing Thread Strength Chart

You need to know if your thread will be strong enough before you get to work on your project. So, it’s crucial to determine the textile size, strength, and metric size, as well as the appropriate needle size. Below are the types of thread and their measurements. 

Thread Types

Polyester Thread

SizeTexStrength (lb)DiameterNeedle Size
15162.11 (0.95 kg)0.004710-12
30303.7 (1.67 kg)0.007012-14
46457.09 (3.21 kg)0.008014-16
697010.13 (4.59 kg)0.010716-18

A polyester thread is used for most outdoor projects, such as tents, tarps, outdoor cushions, and even boat coverings. It has better UV resistance than other threads and has low shrinkage. 

Polyester is resistant to mildew, weather, and abrasion damage. The thread is better suited for outdoor creations, such as creating tents.

However, if the polyester thread is not UV treated, it loses its strength after a certain period. It is better to use UV-treated thread for outdoor projects. 

Nylon Thread

SizeTexStrength (lb)DiameterNeedle Size
15162.22 (1 kg)0.005910-12
30304.88 (2.21 kg)0.008012-14
46457.4 (3.35 kg)0.009414-16
697011.31 (5.13 kg)0.011516-18

Nylon thread helps create furniture, backpacks, leatherwork, purses, and much more. With its versatility, strength to size ratio, and durability compared to other threads. This thread makes it the perfect line for heavy-duty projects.

Nylon is resistant to aging and mildew. It makes nylon perfect for car seats and other auto upholstery. Nylon is also somewhat weather-resistant. However, Polyester can withstand rain and different weather.

Yet, nylon is not heat-resistant and cannot withstand temperatures over 500℉ (260°C). If the thread is directly exposed to sunlight or heat for an extended time, it will melt. 

So, keep any projects made with nylon in a controlled temperature environment. Also, add some protection against ultraviolet rays to preserve the thread.

Cotton Thread

Using cotton thread, you can create quilts, clothing, and some patchwork. It is a natural thread, meaning it uses organic materials. 

Cotton is soft, making it a perfect thread and even fabric to work with. Given its strength, fibers, and medium sheen, you can count on getting a tight seam. 

However, since it has natural fibers, it does not have the same capabilities. Cotton is vulnerable to bugs, mold/mildew and does not age well. You cannot tell if you have high-quality cotton or if you bought low-quality cotton. 

Kevlar Thread

Kevlar thread is used to create high-strength equipment and gear. This thread is made to be fire-retardant, twice stronger than nylon, and even is puncture-proof. Dupont has this a safe thread for first responders to use and also for everyday use.

The only downside I see to Kevlar thread is that it is hard to find in colors other than yellow. However, you can get a brand with multiple military-style colors on Amazon.

Is Nylon Stronger Than Polyester Thread?

Nylon is stronger than Polyester thread. It has more versatility, durability, and higher strength to size ratio. High-durability projects include upholstery and working with leather. Polyester is used for tasks such as the manufacturing of tents.

Is Polyester or Cotton Thread Stronger?

Polyester is stronger than cotton. The Polyester thread is resistant to mildew and moisture, bugs, and mold. The material is more tensile than cotton, making it perfect for heavy-duty projects.

What Is the Best Thread To Use for Sewing?

The best thread to use for sewing is Polyester, as it has low shrinkage and more excellent resistance to ultraviolet rays. It also holds shape well. Polyester will not fade until 20+ years later.

The Gutermann Sew-All Thread is a perfect example of why Polyester is the best thread to work with. This thread is great for hand sewing as it provides versatility and does not lack in quality. Whether you choose to sew by hand or by machine, this thread can get it done.

Do You Need a Special Thread for Sewing Machines?

You do not need a special thread for sewing machines. You need to determine the needle size you are using, the thread size, and what kind of fabric you are using.

A good rule for sewing is to match the thread to the type of fabric you are using. Polyester thread works well with the same material. The same is said for other thread and fabric types.

If you use the wrong thread for your fabric, your project will not last long. To prevent this, use the same material thread as the fabric.

What Does 40 Wt Thread Mean?

40wt thread means 40kg of yarn weighs 1kg (2.2 lbs). You would have to divide the length of the thread by the set weight to get the exact weight of the string.

Superior Threads has an outstanding example of measurements. They also include some excellent information if you need help with sizing and weight.

What Heavy Duty Thread For Canvas?

The best heavy-duty threads to use on a canvas are bonded nylon, bonded Polyester, and kevlar thread.

If you are using nylon thread for your canvas, make sure to keep it indoors since there is no sun protection and keep it away from outdoor elements.

If using polyester thread, use double-bonded polyester thread. It has more UV resistance than nylon and kevlar. Your canvas can be outside in the sun and be protected from the elements.

If you choose to use kevlar thread, go for bonded kevlar. Not only will the thread help resist abrasions with a resin coating, but it can also tolerate high heat (up to 800°F),  so the thread will never overheat.

Bottom Line

The strongest sewing thread is Kevlar thread. However, you should not use it for every project. Always determine what kind of thread you need by the type of project. Here are some questions you could ask yourself:

  • Is this going to be outside? 
  • Do I need this to stretch?
  • Does this thread match with my fabric?
  • Can I use this in more than one color? 
  • What qualities do I need?

Research and ask those five questions to determine what thread you need. It can save you material and money before you make a purchase.

Thanks for reading!

For more, check out 7 Best Ropes for Survival Based on Uses and Situation.

Anne James

Hi, I'm Anne but my grandchildren call me Jelly Grandma. I have over 50 years of experience as a Southern cook and am a retired librarian. I love sharing what I have learned. You can find me on YouTube as well! Just click the link at the bottom of your page. I hope your visit here has been a sweet one.

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