How does a zipper work?

You pull a little tab on your jacket and zzzip — two flappy sides join into one. Pull it back and they fall apart again. How does a zip do that?

Rows of tiny teeth

Look closely at a zip and you will see two rows of little bumps facing each other. These are the teeth. Each tooth has a small hook and a small hollow.

On their own, the two rows just lie next to each other and do nothing. They need a helper to lock them together — and that’s where the slider comes in.

The clever slider

The little tab you pull is called the slider. Inside it there are smooth, slanted ramps called wedges.

As you pull the slider up, the wedges guide each pair of teeth together and gently push them so one tooth hooks neatly into the gap of the other. Tooth by tooth, they click into place — and the zip is closed!

Going back down

When you pull the slider down, a wedge in the middle slides between the rows and pries the teeth apart again, one by one. The two sides come undone and the zip opens.

So a zip never really “sticks” — the slider just hooks and unhooks the teeth as it travels.

Wonder fact: The zip was invented over 100 years ago, but at first it was called the “clasp locker” — the fun name zipper came from the zzzip sound it makes!