What is overlock and why is it a seam type

Short answer: What is overlock? It is a seam type where a machine with several threads trims the edge of the fabric and wraps thread around it in one pass. The result is a seam that does not fray and can give when the fabric stretches. Here is how to recognise it and why it is used.

What is overlock in practice

Overlock is both a machine and a seam. The machine, also called an overlocker or serger, joins several threads so the edge is enclosed in loops of thread. At the same time a blade cuts off surplus fabric, so the seam ends up clean and flat. You can see it on the inside of many garments as a dense row of small loops.

Why overlock counts as a seam type of its own

Overlock is a seam type in its own right, because it is built differently from a plain straight seam. A straight seam is a single row of stitches, while overlock lays thread both along and over the edge. That gives a finished edge, which is why overlock suits knits and other fabrics that fray or curl.

Why overlock suits knits and jersey

Knitted fabrics have to stretch when you move, and overlock can do that, because the thread loops leave room to stretch. That is why you often see overlock in the seams of T-shirts, tops and bamboo sweatwear, where the fabric is flexible. A stiff, straight seam would snap when the fabric was pulled.

How to recognise overlock on your clothes

Turn the garment inside out and look at the seam at the shoulders, sides and armholes. Overlock looks like a row of dense loops or a slightly ruffled edge where the thread wraps around the fabric. The edge is often flat and tidy, and you can pull gently at the seam to feel that it gives.

What overlock says about quality

Asking what is overlock also helps you judge a seam. An even, dense overlock without loose threads or gaps is a good sign, because it holds the edge together through many washes. The seam alone does not say everything, so also look at the fabric and the fit before you choose.

Overlock and comfort against the skin

An overlock seam lies flat, so it bothers the skin less than a thick, stiff edge. Even so, a seam is felt more in a sock or in underwear than in a sweatshirt, which is why flat seams are often used there. It is worth checking in, for example, socks for men, where the toe seam can feel different.

How to look after overlock seams in the wash

Wash clothes according to the care label and avoid pulling hard on wet seams. Turn the garment inside out so the seams are protected from rubbing, and close zips and hooks so they do not catch the thread. If you see a loose thread, snip it off instead of pulling it.

When an overlock seam comes undone

When an overlock seam comes undone, it is often just one thread that has pulled loose, and then a needle and thread or a tailor can fix it. It is worth repairing quickly, before the gap grows. That goes for the seam in long sleeve models too, where the sleeve is stretched and can put more strain on the seam.

Frequently asked questions

What is overlock

Overlock is a seam type where a machine trims the edge of the fabric and wraps thread around it. It gives a finished edge that does not fray and can stretch with the fabric.

Why is overlock used on T-shirts and sweatwear

Overlock gives when you move, and the edge does not fray. That makes it a good match for knitted fabrics such as those in T-shirts and sweatwear.

Can I repair an overlock seam myself

A small opening can often be closed by hand with a needle and thread. For bigger damage or a seam under a lot of strain, a tailor can help so the repair lasts.