Does embroidery thread go bad over time? Polyester, rayon and metallic in storage

Does thread have an expiry date?

No. None of the thread makers we checked prints an expiry date or a shelf life in years, and the two that address it say there is no fixed one. Amann states that "under normal storage conditions, there are no known adverse effects" on the quality of its threads. Sulky answered the rayon question for its own line: "our quality Sulky Rayon Threads do not have a shelf life if stored properly," adding that spools over 20 years old still perform.

The year figures that circulate are not measurements, and they disagree by a factor of ten:

The long answer is right, with a condition attached: a properly stored spool from a reputable maker does not fail on a schedule. The short figures persist because everyone has met the cone that snaps when you look at it, and that cone is real. SignWarehouse explains it: "the difference between thread that lasts decades and thread that dies in two years is almost entirely storage." Light, heat, damp, dust and knocks damage thread; the calendar does not. The useful question is whether a spool passes a test, not how old it is.

Test an old spool in two minutes

Every check is a comparison, so keep a fresh spool of the same fiber and weight beside the old one. Compare rayon with rayon: OESD says Isacord polyester has twice the strength of rayon, so a rayon that feels weak next to fresh polyester proves nothing.

1. Look at the outer wraps. Look for a fade line where the side that faced a window is paler, and for a dull, dusty finish. Graphics Pro notes that dust "can dull thread finishes", and SignWarehouse lists a rough, chalky feel as a warning sign.
2. Snap test from the outside. Pull off about a foot (30 cm) from each spool, wrap the ends around your fingers and pull steadily apart. Per SignWarehouse, good 40 wt polyester "stretches slightly then resists"; bad thread "snaps clean with no fight." Do it three times on each spool.
3. Strip and test again. If the outer layer fails, unwind a few meters (a few dozen wraps) and repeat the snap test. Light and dust attack the outside first.
4. Stitch it. Fit a fresh 75/11 embroidery needle so the needle cannot take the blame, and stitch a satin column and a small fill at your normal speed. Then run an I-test to confirm the balance.
5. If it breaks only at speed, slow down one step. Clean breaks that stop at a lower speed mean the thread is near its limit (see speed settings). Frayed ends with fluff at the needle are a different fault: thread shredding.

What to do with thread that fails

Decide by what the test showed, not by the age of the spool:

Old top thread is often sent to the bobbin. It is a poor home: weakened thread breaks there too, and 40 wt is heavier than the 60 or 90 wt bobbin thread most machines are set for, so the back thickens and tension needs rebalancing. See bobbin thread and prewound bobbins.

Why rayon and metallic age differently from polyester

Rayon: less margin, more sensitive

Rayon is a regenerated cellulose fiber, made from wood; embroidery polyester is a synthetic filament. Madeira says rayon fibers "become weaker while wet," and advises against rayon in work "exposed to long periods of sunlight and UV rays, as it will fade under these conditions." Ricoma says rayon is "sensitive to light and moisture, while polyester can handle tougher conditions." OESD describes Isacord polyester as colorfast to light.

Coats lists "loss of strength due to over-exposure to ultra-violet light" as a risk for thread in general, so polyester is not immune. The point is margin: rayon starts weaker, so the same loss takes it closer to breaking at embroidery speeds. Sulky's 20-year-old spools show that exposure, not time, does it: a rayon spool that lived in a drawer is a better bet than a polyester spool from a sunny windowsill. The polyester vs rayon comparison covers the fibers in use.

Metallic: the core is fine, the surface is not

Madeira's CR Metallic, for example, is 68 percent polyester and 32 percent metallic polyester, so much of it is the same fiber as an ordinary polyester spool. The failure point is the metallized surface, which cracks if it is bent sharply, rubbed or heated (see metallic thread). SignWarehouse says metallic foil wraps "delaminate with age and heat."

So a snap test can pass a metallic whose surface is already lifting. Stitch it instead: a short satin with a fresh metallic or topstitch needle, at the reduced speed metallics need anyway. If it flakes or shreds, the spool is done for visible work, however strong it feels.

How to store thread so it lasts

Makers and trade sources give storage conditions, not lifespans, and their figures overlap closely:

Every range in that table contains 65 to 70°F (18 to 21°C) at 40 to 60 percent relative humidity: an ordinary room kept out of the sun. Garages, attics, vans and shelves over a radiator are where thread goes bad. In practice:

• Cover it. A closed cabinet, drawer or covered rack keeps light and dust off. Madeira warns that surface dust "traps the moisture in the air against the thread and will ruin your supply over time."
• Keep it out of the sun, upright, and do not drop cones. Graphics Pro's minimum is thread stored vertically, at room temperature, out of direct sunlight.
• Rotate stock. Amann recommends "first in, first out" to avoid long storage times: new spools go behind old ones.

Where this stops applying

• Finished embroidery. This page is about thread on the spool. Stitched rayon left in the sun fades whatever the spool's condition. Choose the fiber for the finished piece with embroidery thread types.
• Unknown threads. Inherited spools with no maker or fiber on the label get no benefit from any maker's statement. Test each one before a real job.
• No maker has published a test. The storage figures above are guidance, not aging trials. The bench test, not a number of years, is the evidence.

If a spool passes every check and still breaks, the thread was not the problem: work through thread breaking in order, changing one thing at a time as in the stitch-out tuning method.