Machine embroidery uses a 40 weight embroidery thread on top and a finer dedicated bobbin thread underneath, which is a different combination from ordinary sewing.
Weight. Forty weight is the standard almost every design is digitised for. Sixty weight is finer and suits small lettering and fine detail. Twelve and thirty weight are heavier and used for a bolder, hand-worked look; they need adjusted density.
Polyester or rayon. Polyester is strong, colourfast and survives repeated hot washing, which makes it the sensible choice for children’s clothes, workwear and anything laundered hard. Rayon has a softer, brighter sheen and is traditionally preferred where appearance matters more than laundering. Rayon is weaker and older spools become brittle.
Bobbin thread is deliberately finer, usually 60 weight or lighter, and normally white or black. A full weight bobbin thread builds a ridge on the back of a dense design, which pulls the fabric and puckers it. This is one of the few places where matching top and bobbin thread is wrong.
Metallic thread is a specialist case: it is abrasive and fragile. Use a metallic needle, reduce speed substantially, loosen top tension and let the spool unwind from a stand without twisting.
How the thread comes off the spool matters. Cross-wound spools want a horizontal pin, parallel-wound want a vertical one. The wrong orientation twists the thread as it feeds and causes breaks that look like tension faults.
Buy the colours you use often in larger spools, and keep them out of sunlight — surface fading on a spool shows as a stripe in the stitching.
Questions people actually ask
Can I use ordinary sewing thread?
It will stitch, but it is duller, less smooth and breaks more often at embroidery speeds. For anything you care about, use embroidery thread.
Does the bobbin thread colour show?
Slightly, at the edges, if the top tension is too tight. White under light fabric and black under dark is the usual choice.
Last reviewed 2026-08-11