Embroidery bobbin thread and prewound bobbins: what to use and why

What bobbin thread should you use for embroidery?

For nearly all embroidery, use a dedicated bobbin thread rather than your top thread or an all-purpose sewing thread. Embroidery bobbin thread is usually 60 wt or 90 wt, finer than the 40 wt top, and comes in white and black. The finer thread does three useful jobs:

• A flatter, softer back. Dense designs build thread on the back. A fine bobbin thread keeps that bulk down, which matters on garments worn against skin.
• More length per bobbin. Fewer bobbin changes in the middle of a design, and fewer mid-fill restarts that can leave a visible spot.
• Predictable tension. Machines' embroidery tension settings generally assume a fine bobbin thread.

Bobbin threads come as spun polyester (slightly fuzzy, grips well) and filament polyester or nylon (very smooth, low lint). Both work; filament threads produce less lint in the hook area, and spun threads can be a little more forgiving in tension. Whichever you choose, stay with it, because each change needs a fresh I-test.

When the back shows

For free-standing lace, ornaments, both-sided towels and anything where the reverse is visible, use the same thread in top and bobbin, color matched, and rebalance tension. The one-third bobbin target still guides you, but the goal becomes making both sides look acceptable.

Bobbin sizes and styles

Bobbins that look alike are not interchangeable. A bobbin a fraction of a millimeter too tall, or with a slightly different flange shape, can wobble or bind in the case, which shows up as uneven tension, nests and bobbin errors.

Prewound bobbins

Prewound bobbins are wound at the factory under steady tension, so they are very even and hold more thread than most home-wound bobbins. They come in several constructions:

• Cardboard sides. Thin paper flanges hold the thread in place. Some embroiderers peel them off for tight drop-in cases; others run them as supplied. A bent or delaminating side can catch, so discard damaged ones.
• Sideless. The thread is bonded into a cylinder with no flanges. Very common for commercial L-style bobbins.
• Plastic sides. Behave most like a normal bobbin. Some are meant to be discarded after use; check before you rewind one.
• Magnetic core. Used in many commercial setups; the magnet adds a small, steady drag against the case and can reduce backlash (overspin) when the machine stops.

The main trade-offs are cost and sensor behavior. On some machines the low-bobbin warning depends on the bobbin's design and may not work with a given prewound. For a full cost and quality comparison see prewound vs self-wound bobbins.

Winding your own bobbins well

A self-wound bobbin can perform as well as a prewound, if it is wound evenly. A poorly wound bobbin feeds with uneven drag no tension setting can fix.

1. Start clean. Use an empty bobbin with no thread remnants. Winding over old thread produces a lumpy core.
2. Thread the winder tension guide exactly as shown in the manual. Skipping it gives a soft, spongy bobbin.
3. Wind at moderate speed. Very fast winding can stretch polyester, which later relaxes and changes the drag.
4. Check the shape. The thread should lie level across the bobbin, firm when squeezed, not built up on one side.
5. Do not overfill. Stop before the thread reaches the rim; an overfilled bobbin rubs the case.

Inserting the bobbin the right way

Direction matters. On many drop-in machines the thread must unwind counterclockwise as you look down at the bobbin, and then pass through a slot and under the case spring. On front-loading cases, the bobbin usually turns in the opposite direction to the thread pull as the thread passes under the spring. Your manual shows the exact path. A bobbin inserted backwards often stitches, but with different drag and a tendency to nest or show on top.

After inserting, pull a few centimeters of thread through. You should feel even, light resistance. If it spins freely with no drag, the thread is not under the spring.

Bobbin problems and what causes them

Bobbin thread showing on the face

Often top tension, but also a bobbin not seated under the spring. See bobbin thread showing on top.

Uneven bobbin stripe on the back

Uneven winding, a wobbling wrong-size bobbin, or lint under the spring.

Bobbin error message with a full bobbin

Wrong bobbin type for the sensor, lint over a sensor, or the bobbin not seated. See bobbin errors.

Thread loops on the back after stops

Bobbin overspin. On commercial cases an anti-backlash spring or magnetic-core bobbin helps.

Lint building quickly in the hook area

Spun bobbin thread or cotton top thread. Clean more often; see cleaning the bobbin area.

Changing a bobbin mid-design

If the bobbin runs out mid-fill, most machines let you back up a few stitches before resuming, so the new stitches overlap the old and leave no gap. Back up enough to cover the stitches made after the bobbin ran out (the top thread may have kept stitching without locking). For production, many shops simply change the bobbin at the start of each job or each garment once it is below a set level, which avoids mid-design changes on visible areas. The thread usage calculator estimates bobbin thread per design so you can tell whether a partial bobbin will finish.

For setting the bobbin case itself, see bobbin tension.