Thread is the supply everyone skips past on their way to the fun stuff. You pick the fabric, you pick the pattern, and then you grab whatever spool is closest to the machine. That habit is the number one cause of machine tantrums: skipped stitches, birds’ nests under the fabric, thread snapping mid-seam for no obvious reason. Most of that trouble traces back to using the wrong sewing machine thread for the fiber, weight, or needle you have loaded. Once you know what each thread type is built to do, matching it to a project takes seconds. If you’re still filling out your kit, our guide to sewing tools and notions covers everything else you need on the table first.
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The Fiber Guide
Nearly every spool on the shelf falls into one of three everyday categories, plus a shorter list of specialty threads for specific jobs.
The everyday three. All-purpose polyester is the default modern sewing machine thread. It has high tensile strength, enough elasticity to flex with fabric instead of snapping, and it resists fading from sun, washing, and repeated ironing. It handles heat up to roughly 230°F, so pressing and machine washing won’t degrade it. This is the spool to buy in bulk, and gutermann all purpose thread is a reliable place to start.
Cotton thread, specifically mercerized cotton, is the quilter’s standard. Mercerizing runs the fiber through a caustic solution under tension, which swells the fibers so dye penetrates evenly and strength and sheen both improve while lint drops. Mercerized cotton has almost no stretch, and that’s the point: it matches the shrink rate of natural woven fabric, so pieced quilt seams don’t pucker after washing.
Cotton-wrapped polyester splits the difference. A polyester filament core supplies tensile strength and slight stretch, while the cotton sheath gives it the sewability and heat resistance of cotton, resisting melting or glazing at high sewing speeds. It’s a solid pick for jeans and workwear where you want durability and a classic cotton-like topstitch.
The specialty shelf. Silk thread is a tailor’s tool: fine, strong, and smooth enough that basting stitches press out of wool cleanly, where all-purpose thread would leave a permanent dent. Rayon is the classic machine-embroidery thread, chosen for its silk-like sheen, but it’s comparatively weak and not always colorfast, so it belongs on decorative stitching only, never a structural seam. Hand embroidery is a different product entirely. See our embroidery stitches guide for how floss differs from machine thread.
Metallic thread is stiff and prone to shredding unless paired with a metallic or topstitch needle, whose larger, polished eye reduces friction. Monofilament (invisible) nylon blends into any fabric color, but it has a lower melting point than polyester, so press it on low heat, on the reverse side, or under a cloth. Elastic thread for shirring must be hand-wound onto the bobbin, since a machine winder stretches it too tight and ruins the gathering.
Wooly nylon is a textured, crimped filament that fills a stitch and cushions it instead of leaving a hard ridge, which is why it lives in a serger’s loopers for soft, flat seams on knits and swimwear. Our sergers and overlockers guide covers where wooly nylon goes and what stays in the needles. Round out the shelf with heavy-duty topstitching thread for jeans and bags, and bonded upholstery thread (commonly size 69) for canvas, leather, and outdoor gear.
Thread Weights Explained
This is the part that trips up almost every beginner: thread weight (wt) is a length-based system, and it runs backward from what feels intuitive. The number tells you how many kilometers of that thread it takes to weigh one kilogram. A higher number means a thinner thread, because it takes more length of a fine thread to add up to a kilogram. So 50wt is finer than 40wt, and 40wt is finer than 30wt.
In practice, 50wt cotton or polyester is the standard for quilting piecing and everyday garment sewing. 40wt is the default for machine embroidery and general use, giving strong, visible coverage on decorative work. 30wt is a heavier topstitching and decorative weight for visible stitching. 12wt is the thickest weight that still fits through a machine needle’s eye, used for bold decorative stitching and hand-quilting looks.
Two other systems show up on labels. Tex measures the weight in grams of 1,000 meters of thread, so a higher Tex number means a thicker thread, the opposite relationship of wt. Denier does the same measurement over 9,000 meters and mostly appears on filament threads (Tex and denier convert by a factor of nine). Retail “ticket number” labeling loosely echoes the two but isn’t standardized across brands.
Needle size should scale up with thread weight, and a good rule of thumb is a needle whose eye is roughly 40% larger than the thread’s diameter:
| Thread weight | Needle pairing |
|---|---|
| 50wt all-purpose | 80/12 universal (the standard everyday combo) |
| 40wt embroidery/general | 75/11 to 80/12 |
| 30wt or heavier topstitching | 90/14 to 100/16 topstitching needle |
| 12wt heavy decorative | 100/16 topstitching needle |
| Metallic (any weight) | 80/12 to 90/14 metallic needle |
Metallic thread gets its own needle regardless of nominal weight, because the problem is the coating’s friction against the needle eye, not the thread’s thickness.
Match Thread to Project
Skip the guesswork and go straight to what actually works.
| Project | Thread to use |
|---|---|
| Quilting piecing | 50wt mercerized cotton with an 80/12 needle |
| Garment seams (wovens) | All-purpose polyester, 50wt, with an 80/12 universal needle |
| Knit garment seams | All-purpose polyester in the seam (built-in stretch moves with the knit); wooly nylon in the serger loopers for a soft, flat finish |
| Jeans / visible topstitching | 30wt or heavier topstitching thread with a 90/14 to 100/16 topstitching needle |
| Machine embroidery | 40wt rayon or polyester embroidery thread (polyester for colorfastness and strength, rayon for sheen) |
| Hand embroidery | Embroidery floss (stranded cotton), not machine sewing or machine embroidery thread |
| Upholstery / canvas / outdoor gear | Heavy bonded nylon or polyester, commonly size 69/Tex 70 |
| Invisible hemming | Clear or smoke nylon monofilament, pressed on low heat, on the reverse, or under a cloth |
| Shirring | Elastic thread hand-wound onto the bobbin, regular thread in the needle |
Why Cheap Thread Costs You More
Those bins of five spools for a dollar look like a bargain until you sew with them. Bargain thread is usually spun unevenly, so the diameter varies along its length, creating thin spots that snap under normal machine tension. It’s also fuzzy, because the fibers aren’t tightly twisted, and that fuzz sheds constantly as lint. That lint works into the tension discs and bobbin case, where it builds up, throws off tension consistency, and can even damage the tension spring if someone over-tightens the mechanism to compensate. If your machine is breaking thread or skipping stitches more than it used to, tension and thread quality are the first two things to check, and our guide to how to use a sewing machine covers tension adjustment in more detail.
Old thread goes bad too, even good thread. UV light breaks down the fiber structure and fades the color, while dust adds friction that ends up inside your machine. Thread stored cool, dry, dark, and sealed away from dust can last years, cotton roughly 5 to 7 years and polyester considerably longer, versus thread left in a sunny sewing room or an open basket. To check whether an old spool is still good, do a snap test: hold 6 to 12 inches firmly in both hands and give it a quick, firm pull. Good thread gives a crisp, clean snap. Degraded thread stretches and pulls apart weakly, like a cotton ball fraying apart, and should go in the trash.
On brand tiers, Gutermann and Mettler sit at the premium end, strong, smooth, and color-consistent, with Mettler known for long-staple cotton strength. Aurifil is a well-regarded Italian brand with a huge color range and low lint, though some find it slightly delicate. Coats and Clark is the reliable everyday workhorse found in any craft store, and Superior Threads leans specialty and professional grade, a favorite among longarm quilters. Match the tier to the stakes of the project, and store what you buy properly. A dedicated thread storage box keeps spools out of the sun and dust.
Spool Anatomy Extras
A few more terms worth knowing at the thread aisle. Spun thread twists short staple fibers, cotton or polyester, into yarns and plies two or more together, giving it a soft hand and good glide through fabric. Filament thread is made from long continuous synthetic strands instead of short fibers, giving it a smooth, sleek finish. Core-spun thread combines both, a continuous filament core for strength wrapped in a staple-fiber sheath for a soft, sewable surface. Ply refers to how many twisted strands make up the final thread; most all-purpose thread is 2-ply or 3-ply, and more plies generally means more strength and thickness.
One more trick that solves a surprising number of tension mysteries: how a spool is wound determines which spool pin it needs. Cross-wound spools have thread wound in a crisscross pattern and feed off the end without the spool itself spinning, so they belong on a horizontal spool pin. Stacked spools have thread wound in flat parallel rows and are designed to spin as thread feeds off, so they belong on a vertical pin. Put a cross-wound spool on a vertical pin, or the reverse, and you’ll add unwanted twist that shows up as tangling or inconsistent tension. If a machine that sewed fine yesterday suddenly acts up with a brand-new spool, check that first.
For more projects to put all this thread to use on, our library of 155+ printable PDF sewing patterns is available at Sewing Pattern Secrets’ pattern library.
Frequently Asked Questions
What thread should I use for a sewing machine?
For most general sewing, all-purpose polyester thread, about 50wt, paired with an 80/12 needle, is the safe default. It’s strong, slightly stretchy, colorfast, and low-lint. Switch to mercerized cotton for quilting piecing on 100% cotton, or to topstitching-weight thread for jeans and other visible heavy stitching.
What is the difference between 40wt and 50wt thread?
Thread weight is length-based and inverse, so a higher number means a thinner thread, making 40wt thicker than 50wt. 50wt is the standard for quilting piecing and everyday garment sewing, while 40wt is the default for machine embroidery, giving denser, more visible coverage.
Can I use embroidery thread for regular sewing?
Not for structural seams. Embroidery threads like rayon are built for sheen and color, not strength. They’re comparatively weak, not always colorfast, and prone to fraying under construction-sewing tension. Save rayon for decorative stitching, and use all-purpose polyester or cotton for seams.
Why does my thread keep breaking?
The usual causes are low-quality thread with uneven diameter and excess lint clogging the tension discs and bobbin case, incorrect tension settings, a damaged bobbin case, the wrong needle size, or old degraded thread. Cleaning the tension area, switching to a name-brand thread, and matching needle to thread weight resolve most breakage.
What thread do you use for jeans?
A heavier topstitching-weight thread, commonly 30wt or heavier, in cotton-wrapped polyester or all-polyester, paired with a topstitching needle sized 90/14 to 100/16, which has the larger eye and deeper groove needed to handle the thicker thread without shredding.
Does sewing thread go bad?
Yes. UV exposure, dust, and humidity weaken and fade thread as it ages. A quick snap test, pulling a 6 to 12 inch length firmly, tells you if it’s still good: a crisp break is fine, a weak stretchy pull-apart means toss it. Properly stored thread lasts far longer, cotton around 5 to 7 years and polyester considerably longer, than thread left in sunlight or open air.