Sewing thread is engineered to withstand repeated travel through guides, the needle, and fabric while forming a durable seam. Fibre content matters, but so do ply, twist, surface finish, consistency, and diameter.
Fibre and construction
- Polyester thread is durable, easy to care for, and slightly resilient, making it a common choice for garment construction.
- Cotton thread has little stretch and is used for cotton fabrics and many quilting applications, although its strength may differ from polyester at a similar diameter.
- Core-spun thread wraps fibres around a strong core, often polyester, combining surface character with tensile strength.
- Textured or woolly thread has a bulky structure that gives soft coverage, particularly in overlocker or coverstitch loopers.
Fibre name alone does not establish suitability. Seam function, laundering, pressing temperature, fabric weight, and machine type also matter.
Understanding thread size
Manufacturers use several thread-numbering systems, and their numbers do not all run in the same direction. In one system a higher value may mean a finer thread; in another it may indicate greater thickness. Read the unit or ticket system as well as the number rather than converting by appearance.
Thread should pass through the needle eye without abrasion and suit the needle size. Thick thread in a small needle creates friction and thread breaks; an unnecessarily large needle can leave visible holes.
Upper thread, bobbin thread, and tension
In a domestic lockstitch, the upper thread and bobbin thread form the stitch together. Different threads can be used for particular techniques, but thread tension must place their interlock correctly. Linty, inconsistent, or deteriorated thread can obstruct the thread path and make stitch formation erratic.
Embroidery thread is not automatically a construction thread: sheen and running properties may be optimised for visible embroidery rather than a load-bearing garment seam.