What’s The Strongest Stitch (& Thread) On Sewing Machines?

Most sewing machines have between 10-30 different types of stitches, but which stitch is the strongest stitch? Sometimes you just want to most durable result, that will last as long as possible.

What is the strongest sewing machine stitch? The strongest stitch on a sewing machine is a straight stitch. The straight stitch is very hard to tear, and when combined with tough and long-lasting nylon or polyester thread, we get the most durable result. (not all though).

There are situations where the straight stitch is not the best choice.

Let’s look at the different scenarios.

The straight stitch is the strongest we get

The strongest stitch on the sewing machine

The straight stitch is so strong because of how the stitch will layer the thread.

You get multiple layers of thread on top of each other, and that gives us a very good and solid result. When you try to pull it you will have to tear several threads at the same time. It is almost impossible to tear the fabric along the stitch, and when you pull from each side, you will have the extra layers to keep it together.

The stitch looks like this on a sewing machine:

Straight stitch on a singer

This image is from a mechanical Singer model with a very simplistic user interface.

It’s typically the first stitch in the list you can choose from, and it’s also the most used stitch. It’s what you will use whenever you will sew two pieces of a garment together unless they are stretchy (more on that later in this post).

A way to make the stitch even stronger will be to sew it twice and make sure to go forth and back a few times when you start and finish to secure the seam ends. By doing so you make sure it is extra durable in the ends, which is usually where any fabric will be torn.

The straight stitch mimics the super-durable backstitch which you can only really sew by hand (more on that later.

The strongest hand-made stitch

As we mentioned above the straight stitch is derived from the backstitch. A very popular and easy to do stitch you can sew by hand.

That backstitch lets you go over each area twice. You stick the needle through the fabric and make a loop back, as the name indicated. Then you loop back and then move two stitches forward before you go back again and continues.

The hand-sewn stitch is by far the strongest stitch we can do. Why? Because we can use thicker threads than the sewing machine. The needle-hole and the construction of the sewing machine will not let us use a very thick and durable thread. But by hand, we can choose a bonded 3-ply nylon thread that will be a perfect fit for extra heavy duty tasks.

If you want to add a little extra strength to the stitch you should increase the stitch length. By doing so you also use more thread, and you end up with the strongest possible result.

Good examples for when to use the backstitch with a strong thread:

  • Outdoor gear,
  • Tents,
  • Parachutes,
  • Seatbelts
  • Kites for stormy weather and so on.

All situations where you want to make sure the thread and stitch with not break.

You can get sewing machines that will let you use a very thick nylon thread, but your average household machine will not be up to that task. You will need an industrial sewing machine which is designed for it.

Make sure to have the same strength in both the top thread and the bobbin thread. A “chain” is only as strong as it’s weakest link”, and we want every single stitch (both on the top and bobbin) to be as strong as possible.

What about stretchy fabric?

It’s a bit more tricky to sew a really strong stitch with stretchy fabric.

We cannot use the straight stitch for a stretchy fabric such as fabric with spandex or elastane (also known as “Lycra”. The reason is that if you use a straight stitch with stretchy fabric, the thread will get torn when you stretch the fabric. That will happen or you might remove the fabrics ability to stretch at all because a straight stitch will not be stretchy at all.

For the same reason, we want to use a zigzag stitch for stretchy fabric for the fabric not to tear the thread when the fabric is stretched. When you use the zigzag stitch the fabric can move a little with each stitch, and that’s why zigzag is recommended here.

But the standard zigzag is not as durable as the straight stitch. So we will have to look at an alternative:

The triple Zigzag(Tricot) Stitch:

The triple zigzag is the strongest stitch for stretchy fabric

The triple zigzag is both stretchier and stronger than the ordinary zigzag, and you might have noticed it in underwear such as men’s boxers.

What is the strongest thread for sewing?

Now we know that the straight stitch is the strongest one we can do. Now we will look at the other element to a durable result. The thread.

The strongest threads are made of upholstery nylon. Upholstery thread has a special resin coating which adds to the strength. It’s a product fabricated in the lab, as we will see below.

The reason nylon is so much stronger is found in the chemistry of nylon. On a molecular level, the bonds between the items are just super strong. The molecules are big and tightly knit together. It gives us a very high tensile strength and a thread that will not break easily.

Nylon is a type of plastic called polymer. It’s not a natural product, meaning that you won’t find it in nature. It is fabricated from organic chemicals such as coal or petroleum. You heat it up to a very high temperature, and the result is just amazing.

The most used form of nylon thread is also called Nylon 6-6 or 66 because it is made from two molecules each consisting of six carbon atoms.

Fun Fact
Two other plastic types which are chemically related to nylon are Kewlar and Nomex. Kewlar we know from bulletproof wests and Nomex is a fireproof type of fabric used in own gloves and race car suits.

Nylon thread is almost always used for upholstery work. For outdoor use, you will use a UV protected product in order to protect the colors from the sun. For indoor use, you can also find cheaper alternatives, which are not resistant to the sun. Besides upholstery work, it is also used for projects like the ones we listed earlier in this article (parachutes, seatbelts, tents, outdoor gear etc.).

Other strong threads

Besides nylon, you can also get very durable threads made from cotton. You want to look at the tensile strength, which will often be listed on the packaging for these types of thread.

Other elements that affect the strength of a cotton thread is:

  • The fiber type,
  • thickness
  • Quality of the cotton
  • and how it is made

If you are not planning an outdoor sewing project like a tent, kite etc. or upholstery work, you might be just fine with a standard cotton thread in a good solid quality. Make sure to choose a thin thread and you should be fine.