The Ultimate Guide to Thread

Understand the differences between the most common types of thread—including cotton, polyester, and wool—plus learn how to sew with each.

Photo: Bryan Gardner

Most sewing projects require little more than needle and thread. But have you ever given a second thought to how you choose the latter? It may be a small detail, but the type of thread you work with matters more than you think. As you browse the spools available in store, think about a thread's durability: how it passes through the eye of a needle, winds around a bobbin, pulls with tension, and stitches through layers of fabric into a sturdy knot. Loose fibers will fray and snap, but a well-chosen thread that matches the size, weight, and properties of the fabric you will be sewing will finish the task seamlessly. Choosing the best thread will translate into smooth seams, no breakage, and consistent stitches (and no skipped stitches, if you're using a machine).

Start with the basics: In its simplest form, thread consists of two or more plies of yarn that are twisted together. Thread can be monofilament (meaning one ply) or composed of multiple filaments (two or more plies). Once it's spun, thread can be treated with a special finish to increase its endurance and appearance for project-specific needs: waxy for polyester that allows the thread to slip through fabric with minimal friction or smooth for silk thread that results in low-lint quilting.

Understanding Thread Weight

When choosing your thread, consider its weight (this refers to thickness). The thicker the thread, the more visible your stitches will appear in the fabric. Weight is numbered on the spool: A small number correlates to a thicker thread; a bigger number correlates to a finer thread. The three most common sizes of thread in the U.S. are 30, 40, and 50 wt. (For comparison, all-purpose thread is usually 40 wt.) It's best to know your project and possible strain on the seams before choosing a thread.

Choosing the Right Thread

In the end, it's important to read the instructions of any sewing project, which may recommend a specific kind of thread. Some crafters recommend matching the thread's material to the fabric material, such as cotton thread for natural fibers or polyester thread for synthetic fabrics. Others will suggest basing your choice on color. In most cases, thread should match the fabric. If you can't find an exact match, select a color one or two shades darker. (That is because darker shades blend in more and lighter shades stand out more.) Otherwise, you may want to choose a contrasting color, which is the case in the Japanese mending method of sashiko. Here's our general rule of thumb: the thread should match the size, weight, and properties of the fabric that you will be sewing.

All-Purpose Thread

As its name implies, this thread is suited for almost any sewing project-by hand or on the machine. Normally made of polyester or cotton-wrapped polyester, it's compatible with most fabrics from light to medium weight cotton, linen, and rayon fabrics. With that said, it's not ideal for extremes in either category: very fine sheer fabrics or heavy denim.

Cotton Thread

Good for constructing seams, sewing buttons, or reinforcing tattered buttonholes, this thread is best matched with lightweight to medium weight natural woven fabrics such as cotton and linen. Most varieties of cotton thread are mercerized, which gives it a silky smooth finish but results in it being very taut. Without much give, it's not suggested for mending knits or heavy weight items.

Nylon Thread

Use nylon thread for sewing anything that requires strength and durability: leather, canvas, or even vinyl. Nylon is strong, highly elastic, and won't shrink. However, it's not colorfast, meaning that it will melt under low heat if not properly bonded.

Rayon Thread

As a popular choice for embroidery, thread in this material is best used for decorative stitching. Rayon thread has radiant shine and is fade-resistant. However, the strands break easily, and so it proves not ideal for seams or mending.

Polyester Thread

When sewing stretchy fabrics such as knits or spandex, polyester thread will have the elasticity to match. Being suitable for sewing light to medium weight woven synthetics, polyester withstands moderate heat, won't shrink, and is mildew resistant, which makes it a good choice for mending everything from workout clothes to heavy quilts.

Silk Thread

Soft and fine, silk thread is often reserved for embroidery work. However, it's commonly used for sewing silk and wool, and for basting fabrics. The prime benefit of silk is that it doesn't leave holes, takes beautifully to dyes, and is very flexible, making it an excellent tailoring thread. While strong, it is precious to work with, so be delicate to avoid catching the working thread and inadvertently tearing fabrics.

Wool Thread

Fittingly, thread in this material takes on many of the characteristics of wool fabric: it's soft, durable, and wicks away moisture. It has a lovely texture and good elasticity, and takes well to dyeing. Take care to keep it from getting wet: it's prone to shrinking and weakening when wet. Wool thread tends to be used for embroidery projects and blankets, works best with heavy fabrics such as wool or canvas.

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