The Ultimate Guide to Sewing Thread

Item # X-HT-300422

If you think about it, thread is a very small percentage of the cost of your project, yet it’s 50% responsible for keeping the seams together. Such a small item actually makes a huge difference in the quality and outcome of your sewing project. Everyone knows what thread is and how to use it, but there’s so much more to learn. 

Bonus: Scroll to the bottom for our video summarizing everything you'll learn in this blog!

Thread Characteristics


Thread is woven and spun in different ways depending on the type of thread it is and how it will behave as you sew with it. Z-Twist (Left Twist) thread is the most common thread weave and is standard for almost all single-needle sewing machines. The thread twists to the left, and it’s also known as Standard Twist thread. Z-twist thread is the only type of twisted thread we sell at Sailrite. S-Twist (Right Twist) thread is also known as Reverse Twist. The thread twists to the right and is used in double-needle sewing machines for embellishments and decorative stitches.

Ultimate Guide Sewing Thread 3This illustration helps show the S and Z twist in sewing threads.

When thread passes through your sewing machine, extra twist is applied to the thread by your machine. That’s why it’s crucial to choose the correct thread twist. If an S-twist thread is used in a single-needle machine, the sewing process can actually untwist your thread, causing thread shredding and weak seams. Likewise, you would not want to use a Z-twist thread in a double-needle machine.

Wicking vs. Non-Wicking vs Anti-Wicking

Threads that wick are not treated against water absorption. They will allow water to soak into the thread. For this reason, they are recommended for indoor use only. Non-wicking thread is specially treated to repel water and prevent water absorption. It is recommended for outdoor projects that will be exposed to the elements. It’s designed to provide extra protection against moisture leakage through seams. For best results, non-wicking thread should be paired with water-repellent or waterproof fabrics.

Anti-wicking thread is treated with a special wax coating to prevent seam leakage. It provides a completely waterproof seam. Stagnant water will not seep through seams sewn with anti-wicking thread. It’s also more expensive than non-wicking thread. The anti-wicking thread sold at Sailrite® — Bonded Coats Dabond® — also features high strength and stretch control, UV resistance and resistance to heat, abrasion, saltwater and mildew. Pair anti-wicking thread with 100% waterproof outdoor fabrics.

Fiber Types

Ultimate Guide Sewing Thread 4From left to right: monofilament, nylon, PTFE and polyester thread.

There are a variety of thread fibers that are used throughout the home, outdoor, auto and marine industries. Here’s a brief rundown of the various thread types we offer and their basic characteristics and uses.

Monofilament (Indoor)

Monofilament thread is a type of single-ply, non-twisted nylon thread that is strong and clear. It resembles and feels like fishing line, so you don’t want to use it for garment sewing in which the thread will rub against your skin. It’s very easy to tension, which makes sewing easy. It has a high resistance to abrasion, though it is not flexible like spun nylon. Because it’s clear, it is useful when you want invisible seams, such as with some leatherwork, furniture and upholstery.

Nylon (Indoor)

One of the strongest synthetic threads, nylon is known for its flexibility and stretch. When you sit on a seat or cushion, you want the thread to be able to stretch and recover under your weight. This makes it an excellent choice for indoor cushions and upholstery that will receive a lot of use and abuse, as well as all home sewing applications. Due to its lack of UV resistance, it should not be used in outdoor projects.

PTFE (Outdoor)

Commonly known as Lifetime Thread, synthetic PTFE thread is engineered to be unaffected by UV rays. In fact, it carries a lifetime guarantee and will outlast the fabric used in your sewing project. Because of its superior resistance to UV damage, it is only recommended for applications that will be mostly or permanently outdoors. Unaltered by prolonged exposure to UV rays, pollution, chemicals, weather and more, Lifetime Threads are recommended for outdoor projects including awnings, marine projects, canvaswork, patio umbrellas and much more. Lifetime Threads are the only thread type that is unaffected by bleach.

Polyester (Outdoor)

Our top choice for outdoor projects is UV treated polyester thread. This is by and large the most popular option for outdoor projects because it offers high strength and stretch control while delivering excellent UV stability and abrasion resistance. Polyester is naturally UV resistant, but when treated with an additional UV inhibitor, the thread becomes the second-best option for outdoor applications behind PTFE thread.

All outdoor polyester thread Sailrite carries is UV treated, ensuring the thread will last as long as possible. While polyester will not last as long as PTFE, it has good elasticity, making it great for all outdoor seating and cover applications. Polyester will weaken and degrade if the fabric it’s sewn with is cleaned with a bleach solution.

To learn more about which thread materials are best suited for various indoor and outdoor sewing projects, read our blog “Selecting the Right Thread Material” (#300134XHT). It has everything you need to know about various fiber types and our recommendations.

Thread Thicknesses & Sizes

A thread’s thickness is actually a measure of its weight, not its diameter. This is because thread is spongy, and the diameter is not able to be measured accurately. Diameter is also an ineffective measuring unit because the tightness of a thread’s twist and bonding can affect its thickness. Generally, as a thread’s size increases so does its seam strength and tensile strength.

The most common thread size designations are Tex, denier, weight and commercial sizes (V). Thread size/thickness is based on the ratio of a fixed length of thread to its weight. For example, Tex is the weight in grams of 1,000 meters of thread. So, 1,000 meters of Tex 90 thread weighs 90 grams. To learn more about the different thread size systems, read our blog “Understanding Thread Sizing” (#300088XHT).

Ultimate Guide Sewing Thread 5You can see the difference in thickness of our (left to right) Tex 30, Tex 70 and Tex 135 threads.

At Sailrite, we use Tex sizes. We also organize our sewing threads by use: Indoor, Outdoor and Lifetime. Within these categories, you'll find different thread weights and materials for a variety of uses.

Our Indoor threads are ideal for home décor projects, leatherwork, bags, indoor upholstery, clothing and more. Choose nylon thread in sizes from Tex 70 to Tex 135 and polyester thread in sizes from Tex 30 to Tex 75. Our monofilament thread is also included in this section. It's available in sizes Tex 18, Tex 40 and Tex 52.

The Outdoor category houses our UV bonded polyester threads. Get these threads in sizes from Tex 30 to Tex 135. PTFE/Lifetime threads are also in the Outdoor section; they're available in sizes Tex 92 and Tex 138. Use these thread types for sails, canvaswork, outdoor upholstery, tents, awnings and more.

One thing to note is that some of our polyester threads are suitable for both indoor and outdoor use. Gütermann Tera polyester threads can be used for applications such as upholstery, flags, leatherwork, bags, clothing and shoes that you plan to use indoors and outdoors.

Our heaviest threads, Tex 135 and Tex 138, can only be sewn on industrial machines like the Sailrite® Fabricator®. Heavy-duty machines like the Sailrite® Ultrafeed® and Sailrite® Leatherwork® can handle thread sizes up to Tex 92.

There are plenty of guides out there to help you select the right thread and needle size for your project. In fact, we’ve got a great blog on the topic. To learn how to pair the right needle size with your thread size and fabric, read our blog “Thread and Needle Recommendation Guide” (#300032XHT). The downloadable chart organizes the different thread and needle size options so you can choose the right combination for whatever you’re sewing.

Cone vs. Spool Feeding

The two most common thread feeding systems are cones and spools. Cones hold much more thread than spools. Cones are used for heavier weight threads, whereas spools typically hold home sewing threads. You’ll also notice that on the cones of thread sold at Sailrite, the thread is cross wound, whereas spools of thread are stack wound. Cross-wound thread is wound diagonally on the cone in a criss-cross pattern, resulting in a pattern of “X”s on the cone. In stack-wound spools, the thread has been wound straight with the thread “stacking” one row above the other. This creates a pattern of straight lines on the spool of thread.

The way the thread is wound affects how it is sewn and whether the spool or cone is situated on or next to the sewing machine. Stacked thread spools are placed on the vertical spool pin that sits on the top of your sewing machine. The thread unwinds parallel with the top of the sewing machine in straight, clean lines as you sew. Cross-wound cones of thread are designed so that the thread comes off the top of the cone as you sew. That’s why these larger cones of thread pair with a thread stand that has a crook or hook at the top. The thread loops through this crook so that the thread pulls straight up off the cone as you sew. This feeding method adds an extra twist to the cone of thread, increasing thread strength and easing tension problems.

Using the vertical pin holder for a cone of thread is not recommended. You also don’t want to put a stacked spool of home sewing thread on a thread stand. In both cases, the thread will come off the cone or spool in an unnatural way — not as intended — resulting in thread tangling, breakage, tension issues and an unpleasant sewing experience.

Ultimate Guide Sewing Thread 6See how the thread comes off the cone vertically (left) versus the spool of thread (right) that unwinds horizontally and parallel with the top of the machine as you sew.

Glossary of Thread Terms

Anti-Wicking: A special wax coated thread that waterproofs seams and prevents seam leakage.

Bobbin: A metal cylinder on which thread is wound. Used on the underside of the sewing machine for the bottom row of stitching.

Bonded: A special coating added to resist abrasion, fraying, friction and heat when thread is sewn at high speeds.

Colorfastness: The ability of thread to retain its color over time without fading or running.

Cone: Usually plastic cylinder on which thread is wound for sewing. Larger than a spool and typically meant for heavier weight threads.

Denier: A thread sizing system. The weight in grams of 9,000 meters of thread.

Elasticity: A characteristic of thread that describes its ability to recover to its original length after being stretched by a set amount.

Hembob: Industry term for a pre-wound bobbin and also called belbob and barbob. Better stitch consistency and holds 30% to 50% more thread than a self-wound bobbin.

Monocord: Also known as monofilament, this single-ply thread is created by bonding continuous nylon or polyester filaments together. Features excellent abrasion resistance, high strength, and very little to no twist for lower profile stitch visibility. Thread resembles fishing line and is translucent to blend in with many colors. Stiffer than other threads and not recommended for clothing or seams that will rub against skin.

Non-Wicking: Thread treated with water-repellent properties.

Ply: Technical term for a strand of thread. Most threads are 2-ply or 3-ply.

Putup: Refers to the amount of thread on the spool or cone and is usually listed in ounces.

Seam Strength: The strength of the seam in a sewing assembly. Calculated using a special formula including the thread tensile strength and seam construction, among other factors.

Size: The number designation given to a thread indicating its nominal weight or thickness (for example, Tex 70).

Spool: Small cylinder on which thread is wound for sewing with a rim or ridge at the top and bottom. Smaller than a cone and typically meant for lighter weight home sewing threads.

Stitches Per Inch (SPI): The number of stitches per inch of sewing. SPI affects seam strength.

Tenacity: The relative strength of thread calculated by dividing the tensile strength by the thread’s thickness.

Tensile Strength: The maximum stress a thread can withstand while being pulled before breaking.

Tex: The most consistent thread sizing system. The weight in grams of 1,000 meters of thread.

Twist: Refers to how the separate plies of thread are wrapped or twisted during thread construction.

Want to learn more about thread? Check out this short video and become a thread expert in minutes!