Polyester for almost all garment construction; cotton where you want a natural fibre or a matt finish. For most sewing, polyester is the sensible default.
Polyester. Strong, slightly elastic, resistant to rot and to sunlight, and it takes dye well. The elasticity matters: a seam sewn in polyester gives a little under strain rather than snapping, which is why it suits knits and anything that moves. It also survives washing indefinitely.
Cotton. No stretch, a matt appearance, and it takes very high iron temperatures without any risk. Quilters favour it because it behaves like the fabric it joins, and because a cotton thread will give before a cotton fabric tears. It degrades with age and humidity, which is why old spools snap.
The rule that matters more than either. Match the thread to how the fabric behaves, not only to its fibre. A thread with no give on a fabric that stretches will break. A thread stronger than the fabric will tear the fabric at the seam rather than break itself, which is the worse failure.
Do not mix them top and bobbin. Different stretch under tension means the seam will not balance.
Other threads you will meet. Cotton wrapped polyester, which aims at both. Silk, for tailoring and for basting on fine fabric, because it leaves no mark. Rayon and polyester embroidery threads, which are for sheen rather than strength.
And avoid very cheap thread of either fibre. Lint, breakage and an uneven surface cost more time than the saving is worth.
Questions people actually ask
Which is better for quilting?
Cotton, by convention and for good reason on cotton quilts. Polyester is stronger and perfectly usable, and many quilters piece with it.
Does polyester thread damage natural fabric?
On a seam under heavy strain the stronger thread can cut the weaker fabric over time. It is a real effect but a slow one, and it matters most on antique or delicate textiles.
Last reviewed 2026-08-11