Serger Thread vs Sewing Thread: Picking the Right Spool

Quick Answer

For serging and overlocking, use a cone of serger thread — typically 50wt, 100% polyester, and wound in large yardage. For piecing, quilting, and garment construction on a sewing machine, use a spool of sewing thread matched to your fabric and needle. You can use sewing thread in a serger in a pinch, but only if the spool feeds cleanly and you accept more frequent changes and slightly weaker seam coverage.

Why Put-Up Matters More Than You Think

A serger runs three or four threads at once and consumes yardage far faster than a sewing machine. That is why serger thread is sold on cones — often 3,000 yards or more — while sewing thread comes on smaller spools measured in hundreds of yards. The cone shape also feeds smoothly from a stand behind the machine, which reduces drag and tension spikes.

If you try to serge with a standard spool, you will spend more time swapping spools than sewing. A 500-meter spool of Mettler Silk-Finish Cotton Thread 50wt in White is a sensible size for piecing and quilting, but it is not sized for the volume a serger demands. The trade-off is clear: cones cost more upfront but reduce interruptions and keep seam quality consistent.

50wt vs 40wt: What Changes at the Needle

Thread weight works inversely: a higher number means a finer thread. Most serger threads are 50wt because that size balances seam strength with bulk — it lies flat in the overlock stitch and does not add unnecessary thickness. A 40wt thread is heavier and can be useful for decorative serging or when you want a more visible seam, but it may require tension adjustments and can overwhelm lightweight fabrics.

For standard overlocking on knits, wovens, and light-colored garments, stay with 50wt. Maxi-Lock Serger Thread 50wt 3000 yds in Eggshell is a good example: the soft off-white tone suits bridal, lingerie, and light garments where pure white would be too stark. The 100% polyester construction adds strength and colorfastness, and the smooth, lint-free finish helps keep serged seams clean and consistent.

Can You Use Sewing Thread in a Serger?

Yes, but with caveats. A serger can physically run sewing thread, and some sewists do it for color matching or when they run out of cone thread mid-project. The problems are practical: small spools run out quickly, spool shape may not feed evenly from a cone stand, and finer or more fibrous threads can shed lint into the tension discs.

If you must substitute, use a smooth, low-lint thread and test on scrap fabric first. Mercerized cotton like Mettler Silk-Finish Cotton Thread 50wt in White is smooth and consistent, but cotton has less stretch than polyester — so it is a better match for stable wovens than for stretchy knits where you want seam recovery. For everyday serging, a dedicated polyester cone remains the lower-risk choice.

Fiber and Finish: Polyester vs Mercerized Cotton

Polyester serger thread brings stretch, strength, and colorfastness — properties that matter when seams need to move with the fabric. It is the default for overlock machines because it resists breaking under tension and holds color through repeated washing. Maxi-Lock Serger Thread 50wt in Eggshell is 100% polyester and designed for serging, overlocking, and coverstitch machines.

Mercerized cotton, such as Mettler Silk-Finish Cotton Thread 50wt in White, has a silky sheen and added strength from the mercerization process. It is a sewing-room staple for quilting, piecing, and garment sewing where you want a natural fiber against the skin or a matte-to-satin finish. The trade-off: cotton has less give, so it is not the first choice for high-stretch overlock seams.

When the Fabric Decides the Thread

Your fabric often makes the thread decision for you. For quilting and piecing, a 50wt cotton like Mettler Silk-Finish gives you smooth, consistent stitches and a 500-meter spool that means fewer changes. For serging knits or finishing seams on garments, a 50wt polyester cone like Maxi-Lock keeps up with the machine and the yardage.

If you are working with challenging fabrics — velvet, leather, or multiple layers — the thread is only half the equation. A walking foot such as the Bernette 08 Walking Foot uses an upper feed dog that syncs with the machine’s lower feed dog to move fabric evenly. That reduces shifting and gives you smoother stitching, which in turn lets your thread do its job without fighting the feed.

Trade-Offs at a Glance

• Cone vs spool: Serger cones hold thousands of yards and feed smoothly from a stand; sewing spools hold hundreds and may drag or run out mid-seam. Choose cone thread for overlock machines; choose spools for sewing machines.
• 50wt polyester vs 50wt cotton: Polyester adds stretch and colorfastness for serged seams; mercerized cotton adds a silky finish and natural hand for piecing and quilting. Match fiber to fabric movement: polyester for knits and serging, cotton for wovens and quilting.
• Substituting sewing thread in a serger: It can work for a short seam or color match, but expect more frequent changes, possible feed issues, and less seam recovery on stretch fabrics. Keep a cone of serger thread on hand so substitution stays the exception.
• Feed control vs thread choice: A walking foot like the Bernette 08 syncs upper and lower feed dogs to move challenging fabrics evenly, reducing the chance that thread tension problems are actually feed problems. If stitches look uneven on tricky fabric, check your foot before blaming the thread.

Products That Fit This Comparison

• Maxi-Lock Serger Thread 50wt 3000 yds – Eggshell: Maxi-Lock Serger Thread 50wt 3000 yds – Eggshell is 100% polyester, 50wt, and sold as a 3000-yard cone for serging, overlocking, and coverstitch machines. The large cone and polyester fiber match the speed and stretch demands of a serger, while the eggshell tone avoids the harshness of pure white on light garments.
• Mettler Silk-Finish Cotton Thread 50wt 500M – White: Mettler Silk-Finish Cotton Thread 50wt 500M – White is mercerized cotton on a 500-meter spool, suited to piecing, quilting, and general sewing. The smooth, lint-free cotton gives clean stitches for sewing-machine work, but the smaller spool and cotton fiber make it a poor match for high-volume serging.
• Bernette 08 Walking Foot: Bernette 08 Walking Foot features an upper feed dog that works in sync with the machine’s lower feed dog to move fabric evenly. Even feed reduces fabric shifting on challenging materials, so your chosen thread can form consistent stitches without tension surprises.

Which Spool Should You Buy?

Best for

• Serging, overlocking, and coverstitch work on knits, wovens, and light-colored garments
• Sewists who want fewer spool changes and consistent seam coverage
• Projects where polyester strength and colorfastness matter

Not for

• Quilting and piecing where a mercerized cotton finish is preferred
• Hand sewing or detail work that needs a small spool
• Stretch fabrics if you plan to substitute cotton sewing thread in the serger