Last updated: August 22, 2026
Thread is the part of sewing that nobody researches until something goes wrong. You buy a spool that matches the fabric, wind a bobbin, and it works or it does not. When it does not, the thread snaps every few inches, the seam looks fuzzy, and the obvious suspect is the machine, because the thread is the one component that seems too simple to be at fault.
It is not simple. A spool carries a fiber, a weight number and a construction, and all three change how a seam behaves. This page explains what the numbers mean, why a bargain bin cone can break on a machine that sews perfectly with the spool next to it, and which thread belongs on which job.
This article contains affiliate links. If you buy through them, we may earn a commission at no extra cost to you. Learn more.
Quick Answer
What sewing machine thread should you use?
- An all purpose polyester thread handles the great majority of home sewing, from garments to bags to mending.
- The weight number runs backward. Superior Threads explains that a thread is 40 wt when 40 kilometers of it weighs one kilogram, so a higher number means a finer thread.
- Tex runs the other way: it is the weight in grams of 1000 meters, so a higher Tex number means a thicker thread.
- Match the needle to the thread. Heavier thread needs a bigger eye, which is why topstitching wants a larger needle.
Bottom line: one good all purpose polyester covers most of your sewing. Add a heavier thread only for seams that are meant to be seen or pulled hard.
The Three Things Printed on a Spool
Every spool tells you a fiber, a weight and often a length, and those three decide how it behaves. Fiber decides stretch, heat tolerance and how it ages. Weight decides how thick the line of stitching looks and which needle it needs. Length just tells you whether the spool will finish the job.
What is usually missing from the label is construction, meaning how many plies are twisted together and whether the thread has been mercerized or glazed. That is the part that separates a smooth thread from a fuzzy one, and it is the reason two spools with the same number can behave very differently on the same machine.
Why Cheap Thread Is a Real Category
Very cheap thread tends to be short staple, loosely spun and full of fine hairs. Those hairs come off in the tension discs and under the needle plate as lint, and the thread itself snaps at the point where the eye of the needle heats it. The seam it does make looks slightly furry rather than crisp. This is a genuine difference, not brand snobbery.
Thread Weight Numbers, and Why They Run Backward
The number on a spool is a density measure, not a thickness. Superior Threads explains the weight system directly: a thread is labeled 40 wt when 40 kilometers of it weighs one kilogram. Because the length goes up as the thread gets finer, a lower number means a heavier thread. So 40 wt is heavier than 50 wt.
Tex works the other way and is easier to reason about. Tex is the weight in grams of 1000 meters of thread, so if 1000 meters weighs 25 grams it is a Tex 25, and a higher Tex is a thicker thread. Denier uses the same idea over 9000 meters instead.
Which Thread for Which Job
Most home sewing runs on one all purpose polyester and occasionally borrows something heavier. The table lines up the common categories with the work they suit and the needle size that normally goes with them, so you can see where the jump happens.
| Thread | Typical weight | Where it belongs | Needle it usually wants |
|---|---|---|---|
| All purpose polyester | Around 50 wt | Garments, bags, mending, general seams | 80/12 to 90/14 |
| All purpose cotton | Around 50 wt | Quilt piecing, natural fiber wovens | 75/11 to 80/12 |
| Quilting thread | 40 wt to 50 wt | Piecing and machine quilting | 75/11 to 90/14 |
| Topstitch thread | Heavier, Nm 30 class | Jeans seams, buttonholes, visible stitching | 100/16 upward |
| Fine or bobbin thread | 60 wt and finer | Lightweight fabric, bobbin fill | 70/10 to 80/12 |
The topstitch pairing follows the manufacturer guidance for that thread class. Gutermann lists its Top Stitch thread as 100 percent polyester in a Nm 30 designation and directs users to a needle from 100/16 to 120/19 with a matching Sew All thread in the bobbin. The other rows are conventional pairings, not measured results.
Polyester or Cotton, in One Paragraph
Polyester has a little give, resists abrasion well and holds up in the wash, which is why it is the default for clothing and anything that flexes. Cotton has almost no stretch, presses beautifully flat and is the traditional choice for quilt piecing, where a seam that does not move is an advantage rather than a fault.
The old warning that polyester thread cuts cotton fabric belongs to a different era of thread manufacturing and is not a useful rule for a modern home sewer. The practical version of the choice, including heat, shrinkage and where each one lets you down, is in polyester or cotton thread.
Why Thread Breaks, and What Is Usually Behind It
Thread breaking is rarely a thread quality problem on its own. The usual chain is a threading path that skipped the take up lever, a burr on a needle that struck a pin, tension set far too high, or an old spool that has gone brittle. Rethreading with the presser foot up is the free first move and it fixes this more often than anything else.
The Spool Itself Can Be the Problem
Cross wound spools want to feed off the top from a vertical or horizontal pin depending on the winding, and a spool feeding against its winding will jerk and snap. Look at how the thread is laid on the spool and try the other pin. That single change resolves a lot of breakage that people spend an evening blaming on tension.
Old thread is the other quiet culprit. Thread that has spent years in sunlight loses strength, and the way it is stored matters more than its age alone. The full order of checks lives in our page on thread that keeps breaking, and storing thread covers why the inherited spools snap.
Frequently Asked Questions
What is the best all purpose sewing machine thread? A good quality polyester in the all purpose weight suits nearly every home project, because it has slight give, wears well and comes in a huge color range. Cotton is the exception worth owning if you piece quilts.
Is a higher thread weight number thicker or thinner? Thinner. Superior Threads defines a 40 wt thread as one where 40 kilometers weighs a kilogram, so the number rises as the thread gets finer. Tex is the reverse, since it measures grams per 1000 meters.
Should the bobbin thread match the top thread? Usually yes, in weight and fiber. Mismatched weights make the stitch balance drift and can look like a tension fault. Gutermann is explicit about this for its heavy topstitch thread, directing users to a standard Sew All thread in the bobbin instead.
Can I use serger thread in a regular machine? It is possible for basting but not a good habit. Serger cones are usually a lighter, softer thread built for four thread loops rather than a lockstitch seam, so a construction seam sewn with it is weaker than it should be.
Why does my thread shred right at the needle? Almost always a needle problem: too small an eye for the thread, or a burr from a strike. Fit a fresh needle a size larger and see if it stops. Our needle guide covers eye size and thread pairing.
Does thread expire? Not on a date, but it weakens with light, heat and damp. Polyester lasts far longer than cotton in storage, and sunlight is the biggest single enemy. The practical storage rules are in storing thread.
The Bottom Line
One good all purpose polyester covers most of what you sew, the weight number runs backward so a lower number means a heavier thread, and the needle has to grow when the thread does. When thread breaks, rethread first and change the needle second, because the spool is usually innocent. Read next: polyester or cotton thread, our needle buying guide for the pairing, and topstitch thread for seams that are meant to show.