Polyester or rayon embroidery thread? And what about 40 wt vs 60 wt, bobbin thread and needles?

Polyester vs rayon: what is the practical difference?

Both are continuous-filament threads made for embroidery machines; both are shiny and cover well. The difference is the fiber. Rayon (viscose) is regenerated cellulose: very soft, high sheen, drapes beautifully. Polyester is synthetic: slightly stronger, stretchier and chemically resistant.

For someone selling embroidery, it comes down to this:

A shop doing uniforms, towels and baby gifts can run entirely on polyester. If you do fine shirting, handkerchiefs and heirloom pieces, keep a set of rayon in your most-used colors. What does not work is mixing the two in one design: the sheen difference shows under light.

What do 40 wt, 60 wt, 30 wt and 12 wt mean?

Thread weight is a size system in which a higher number means a thinner thread. It is the opposite of intuition, so memorize it: 60 is finer than 40, which is finer than 30.

40 wt is the worldwide standard. Embroidery software, including Meus Bordados, calculates satin and fill density for it. If you change weight without changing density, the result is thin coverage (finer thread) or a stiff, bulletproof patch (heavier thread).

• 40 wt: general use. Names, logos, baby items, uniforms. The default.
• 60 wt: finer. Letters 3/16 to 1/4" tall, fine detail, delicate outlines, light fabrics. Allows more stitches per millimeter without bulk. Also used in the bobbin.
• 30 wt: heavier. Adds loft and covers faster with fewer stitches; nice on large lettering and rustic looks. Needs wider stitch spacing and a 90/14 needle.
• 12 wt: very heavy, hand-embroidery look. Only with designs digitized for it and a 100/16 or 110/18 needle.

Tip: When switching from 40 to 60 wt in Meus Bordados, reduce the satin spacing (for example from 0.40 to 0.32 mm) to keep coverage; when switching to 30 wt, increase it. The setting is under Object properties. See stitch types and settings.

Which thread goes in the bobbin?

The bobbin does not take the top embroidery thread. It takes a dedicated thin thread, usually 60 to 90 wt polyester or cotton, in black or white. Thin because the bobbin is small and needs to last; black or white because it never shows on the right side.

You can buy cones of bobbin thread to wind yourself or prewound bobbins already filled for your machine. Prewounds have even tension and save time; they are the choice of anyone stitching in volume. Check the size (Class 15 / size A on most home machines, L or M on many commercial ones) before ordering.

The back-side rule: bobbin thread should show in the center of a satin column, taking about one third of the width, with top thread on both edges. Bobbin showing on the front means top tension is loose or bobbin tension tight. No bobbin showing on the back at all means top tension is too tight and the design will pucker.

Watch out: White bobbin thread on a dark garment can peek out at letter edges if tension is off. On black garments, use black bobbins. Changing bobbin color per job is cheaper than redoing it.

Which needle for which fabric?

Embroidery needles have a larger eye and a deeper groove than sewing needles so the thread glides without heating. The metric number is the shaft diameter in hundredths of a millimeter (75 = 0.75 mm); the second number is the US size. Use the finest needle that works with the thread: a heavy needle leaves visible holes and pushes the fabric.

The point matters as much as the size: sharp for wovens, ballpoint (SUK) for knits, and titanium-coated needles for high-volume work because they last longer.

How often should you change the needle, and how do you store thread?

• Needle: change it every 8 to 10 hours of stitching, when moving from heavy to fine fabric, and whenever thread starts breaking for no obvious reason. A worn point looks fine to the eye but shreds thread and pulls fabric fibers.
• Thread: keep it away from sun and dust. Rayon absorbs humidity and weakens in damp rooms; polyester is more forgiving. Cones that have been open for years (especially rayon) break more.
• Colors: a shop starts well with 12 to 20 colors of 40 wt polyester (white, black, gray, red, navy, royal, kelly green, gold, pink, metallic gold and silver, brown, tan) and fills in as orders come.

When pricing, remember thread is a small part of the cost: the Meus Bordados viewer shows thread used in meters when you open a design, and a 5,000 m cone covers dozens of jobs. What drives price is machine time, as we show in how to price custom embroidery.

How do you fix the most common thread problems?

Thread breaks every few minutes

In order of likelihood: worn or wrong needle, thread path off a guide, top tension too tight, old cone, design density too high. Change the needle first, rethread with the presser foot up, then look at tension.

A bird's nest forms underneath

The top thread is not seated in the tension discs (threaded with the presser foot down) or the bobbin is in backward. Rethread with the foot up and check the bobbin direction in the manual.

Bobbin thread shows on top

Top tension loose or bobbin tension too tight. Adjust top tension half a step at a time first; bobbin case tension almost never needs to change.