For sewing clothes, use polyester thread: an all-purpose polyester (often labeled Tex 27 or 100 % polyester, 40 or 50 weight) is stronger than cotton, stretches a little so seams do not snap on knits or fitted garments, and does not shrink or fade in the wash. Cotton thread is the better choice for quilting, for heirloom and historical sewing, and for garments that will be dyed after sewing. For everything else, a good polyester wins.
How do cotton and polyester thread compare?
| Feature | Cotton thread | Polyester thread |
|---|---|---|
| Strength | Moderate | High; about 30 % stronger at the same size |
| Stretch | Almost none | 10–15 %; seams give with the fabric |
| Shrinkage | Can shrink 1–2 % in hot washes | None |
| Colorfastness | Good; can fade over years | Excellent |
| Heat | Takes a hot iron | Melts under a very hot iron; fine at cotton settings in practice |
| Lint | Sheds lint in the machine | Very little |
| Surface | Matte, soft | Slight sheen, smooth |
| Fabrics | Cotton, linen, quilting cotton, silk | Everything, including knits and synthetics |
| Price | Medium | Low to medium |
Both come in similar sizes. "All-purpose" from the big thread brands is usually a 40 or 50 weight, suitable for light to medium fabrics; a 30 weight is heavier for topstitching; a 60 or 80 weight is fine for lingerie and heirloom work. The lower the weight number, the thicker the thread. The post on sewing machine needles and thread pairs each thread size with a needle.
Why is polyester the default for garments?
Three reasons. First, strength: a polyester thread of the same size holds more before it breaks, so seams at the crotch, armhole and side of a fitted garment last longer. Second, elasticity: polyester stretches 10–15 % and recovers, which lets a seam on a knit or a fitted woven move with the body. A cotton seam in a stretch jersey pops the first time you pull the garment over your head. Third, care: polyester does not shrink or bleed, so a seam sewn with it looks the same after fifty washes.
Modern all-purpose polyester is also spun finely enough to disappear into cotton and linen. Thirty years ago cotton thread was the obvious choice for a cotton garment; that is no longer true.
When is cotton thread the better choice?
Cotton thread earns its place in a few situations.
- Quilting. Cotton thread wears at the same rate as cotton fabric, so a strong polyester thread does not cut through the fabric over decades. Quilters also like the matte finish and the way it beds into the fabric.
- Heirloom, historical and costume sewing. For a garment that should be made as it would have been, cotton or silk thread is correct, and cotton has the right low sheen.
- Dyeing after sewing. Cotton thread takes the same dye as cotton fabric; polyester stays white. If you sew a garment in undyed cotton and dye it afterward, use cotton thread.
- Very hot pressing. Cotton thread cannot melt. If you press linen at full heat with a lot of steam and have scorched polyester before, cotton removes the worry. In practice, a polyester thread survives normal cotton and linen pressing without trouble.
- Basting. A cotton basting thread breaks easily when you pull it out, which is the point.
Cotton thread is also lovely for hand sewing: it does not twist and knot the way polyester can, and it glides through cotton fabric. Run it through beeswax for hand hems and buttonholes.
Which thread for knit fabrics?
Polyester, without exception. The seam has to stretch at least as far as the fabric, and a cotton thread does not stretch. Combine it with a stretch stitch (a narrow zigzag or lightning stitch) and a ballpoint needle, as the guide to sewing knit fabrics explains. Woolly nylon or textured polyester in the loopers of a serger gives a softer, stretchier edge on swimwear and lingerie.
Does thread choice affect tension and puckering?
Yes. Cotton thread is fuzzier and sheds lint in the bobbin case and under the throat plate, which eventually drags on the thread and spoils the stitch; clean the machine more often when you sew with cotton. Polyester is smoother and can slide a little in the tension discs, so a thread that behaves on one machine may need the top tension raised a notch on another.
Puckered seams on fine fabric are often a thread problem rather than a tension problem: a thick thread in a fine fabric pushes the yarns apart. Drop to a 60 weight polyester and a 70/10 needle for lawn, voile and silk. If a seam still puckers, the post on sewing machine tension problems walks through the other causes.
Use the same thread top and bobbin unless you have a reason not to; mixing a cotton top with a polyester bobbin is a common cause of a seam that looks fine on top and loops underneath.
What about serger thread, topstitching thread and silk?
Serger cones are usually a finer polyester (around Tex 24) spun for speed and low lint. It is fine in a serger, where three or four threads share the load, but a little weak and lint-free for a sewing machine seam that relies on one thread; keep it to the serger, or use it in the bobbin.
Topstitching thread is a heavy polyester or polyester-wrapped thread, about three times the thickness of all-purpose. Use it in the needle only, with a 90/14 or 100/16 topstitch needle and all-purpose thread in the bobbin, and lengthen the stitch to 3–3.5 mm. It is the thread for jeans, bags and visible stitching on trousers and jackets.
Silk thread is strong, fine and elastic, and presses flat into the fabric. It is the thread of choice for fine wool and silk garments, hand-sewn hems and tailoring, at a price that keeps it out of everyday use.
Cheap bargain-bin thread, whatever the fiber, is the thread to avoid: it is uneven, weak and linty, breaks in the machine and shows every variation in tension. A reel from an established thread maker costs little more.
Which should you choose?
- Everyday garments in wovens and knits: all-purpose polyester, 40 or 50 weight. One reel of a matching color top and bobbin.
- Fine fabrics (lawn, voile, silk, chiffon): 60 weight polyester or silk thread with a 60/8 or 70/10 needle.
- Jeans, canvas, bags: all-purpose polyester for construction; topstitching thread in the needle for the visible rows.
- Quilts and anything you will dye: cotton thread, 40 or 50 weight.
- Costume and heirloom work: cotton or silk.
- Hand sewing: cotton or silk, waxed; polyester if the garment is a knit.
- Serger seams: polyester cones; add woolly nylon in the loopers for swimwear.
Buy the color under daylight by laying a strand across the fabric, not the whole reel: a strand looks a shade lighter than the reel, and a thread one shade darker than the fabric disappears better than one shade lighter.