Embroidery thread guide: polyester vs rayon, weights and colour matching

For most machine embroidery, use 40 wt polyester or rayon embroidery thread on top, a finer 60 or 90 wt bobbin thread underneath and a 75/11 embroidery needle. Choose polyester for anything that is washed often or bleached, such as children's clothes, towels and workwear. Choose rayon when you want a softer sheen on items that won't see bleach.

Polyester vs rayon: what the data sheets say

Both are continuous-filament threads with a high shine, and both sew any normal design. Madeira's own data sheets for its 40 wt threads show where they differ: polyester is about twice as strong and tolerates chlorine bleach within limits, while rayon must not be bleached. Wash temperature and light fastness are rated the same.

Figures from the Polyneon 40 and Classic 40 data sheets. Other brands publish different numbers, but the pattern is the same across manufacturers.

When polyester is the safer choice

Madeira recommends polyester for "children's wear, workwear and any other items that must be frequently cleaned", and for hotel towels and chef's whites that get bleached. Madeira USA adds that polyester holds up under heavy use and commercial laundering, and that rayon gets weaker while wet. If an item goes in the wash every week, polyester is the low-risk pick. For bath and kitchen towels, see embroidering towels.

When rayon makes sense

Rayon's sheen is softer and it feels supple even in dense areas. It suits cushions, wall hangings, table linen and fashion pieces that are washed gently. Madeira's US guide is more cautious than the data sheet: it advises a warm wash with mild detergent and no whiteners or bleach for rayon. Follow that advice for anything you care about.

Which thread weight: 30, 40 or 60?

The weight number is a thickness label, and the lower the number, the thicker the thread. 40 wt is the standard most designs are digitized for, including ours: our fills are laid 0.40 mm apart, the usual density for 40 wt. Use 60 wt for small text and fine detail, and 30 wt for bold, heavy effects.

Lettering shows the difference best. According to Madeira USA, the smallest block letters you can sew with 40 wt are about 6 to 7 mm high, while 60 wt allows letters down to about 3 mm. That matters for monograms and small names.

Weights are not a precise unit. Even within one manufacturer, Amann's brochure lists "40" threads of slightly different thickness. Treat the numbers as a ranking, not a measurement.

Do you need special bobbin thread?

Yes. Embroidery bobbin thread is much finer than the top thread and stays on the back of the work. Brother's accessory catalogue says to use "the appropriate machine embroidery bobbin thread" for best results. Common weights are 60 and 90 wt, mostly in white or black.

The bobbin size matters as much as the thread:

• Prewound bobbins save winding but must match your bobbin class. Brother's PWB350 bobbins carry 90 wt thread and are "not for use with Brother sewing or embroidery/sewing combo models".
• Class 15 is not L-style. Brother describes its SA156 as a Class 15 bobbin, and Sulky's staff match Class 15 to their "Type A" prewound bobbins, not "L".
• When in doubt, follow the manual. It names the bobbin type and the bobbin thread weight your machine is set up for.

Needles that suit the thread

A 75/11 embroidery needle is the standard for 40 wt thread, and Brother's support pages recommend the same for its machines. An embroidery needle such as Schmetz's 130/705 H-E has a medium ball point and a wider eye and thread groove than a universal needle.

• Heavy fabrics (denim, puffy foam): Brother recommends a 90/14, because a 75/11 may bend or break.
• Knits: use a ballpoint embroidery needle. Madeira USA warns against sharp needles on knits. Brother does not recommend its gold ballpoint 90/14 sewing needles for embroidery, so pick an embroidery-system ballpoint.
• Metallic thread: a metallic needle (Schmetz H-MET) or topstitch needle, both with a 2 mm eye.
• Replace it often. The Schmetz Needle ABC recommends a new needle after about 8 hours of sewing or at the start of each project.

How do you match colours between thread brands?

Conversion charts get you close, but rarely exact. Every manufacturer we checked says so: Amann's Pantone-to-Isacord list gives the "closest available" colour and tells customers to "use their own judgement", and Madeira UK states that "exact colour matches cannot be guaranteed". Two neighbouring shades in one brand can map to the same shade in another.

The file you stitch adds another layer. Some formats store thread colours and some don't: Ink/Stitch's documentation notes that DST stores no colour information at all, so any colours a program shows for a DST come from the program, not the file. The file formats guide explains which format keeps what.

A practical routine:

1. Use the design's thread list as the reference. Our designs come with a thread chart in sewing order, with a colour name and stitch count for each colour, and the ZIP download adds a colour sheet.
2. Match against real thread, a printed thread card or the spools you own, not a screen. Monitors and printouts are unreliable for colour.
3. Accept near matches for small areas. A slightly different blue in an eye won't show. A large fill or a brand colour deserves a test stitch.

To check what a file contains before you start, open it in the free embroidery file viewer: it lists the colours, stitch count and real size.

Tension check: the one-third rule

Good tension shows on the back of a satin column: the bobbin thread should form roughly the middle third, with top thread on both sides. Amann and Madeira both state this rule, and Madeira USA describes it as "1/3 bobbin and 2/3 top thread color on the underside."

If too much bobbin shows underneath, or bobbin thread pokes through on top, Madeira USA points to a bobbin that is too loose or a top thread that is too tight. Polyester also needs slightly more top tension than rayon, so a machine set up for one may need a small adjustment for the other.

Metallic thread without the breaks

Metallic thread breaks and kinks more than polyester or rayon, but a few changes help. Madeira's guidance for its metallic threads: slow the machine to 650 to 750 stitches per minute, reduce both top and bobbin tension compared with polyester, use a new needle, and choose designs that are not too dense and have no sharp angles. A thread net over the cone stops the thread from kinking as it unwinds.

Troubleshooting thread problems

Store thread in a cool, dry, dust-free place out of direct sunlight, as Madeira USA advises. If you are just getting started, the beginner's guide to machine embroidery puts thread, needles and stabilizer together into a first project, and embroidering T-shirts and knits covers the needle and backing choices for stretchy fabric.