How do I sew in an invisible zip?

An invisible zip has its teeth curled round to the back of the tape, so when it is closed the teeth sit behind the fabric and nothing shows on the right side except a plain seam. That is what makes it look good and it is also what makes it awkward: you have to stitch right up against a coil that is trying to curl away from you, on a seam that does not exist yet.

What you'll need

• An invisible zip long enough for the opening plus a few centimetres
• An invisible zip foot
• A regular zip foot, for closing the seam below
• An iron
• A seam ripper

Step by step

1. Buy a zip longer than the opening.At least 5cm longer. The slider has to be able to move above the top of the opening while you sew, and the excess is simply left at the bottom inside the seam allowance. A zip cut exactly to length cannot be sewn.
2. Leave the seam open.Do not sew the seam below the zip yet. Finish the raw edges of both pieces if the fabric frays, but leave them unjoined. Everything about this technique depends on being able to lay each side flat.
3. Press the coil flat.Open the zip and press along the coil from the wrong side of the tape with a cool, dry iron, uncurling the teeth so they lie flat. Do this gently and test on the tape end first — zip coils are plastic and will melt. This step is what lets the foot ride the coil properly.
4. Mark the zip position.Mark the seam line on both garment pieces, and mark on the zip tape where the top of the opening will be — usually a little below the raw edge to leave room for a facing or a waistband.
5. Pin the first side face down on the right side of the fabric.Open zip, teeth pointing towards the fabric, tape edge along the seam allowance edge, coil sitting on the seam line. Pin or tack. Tacking is worth the extra minutes on anything slippery.
6. Stitch with the invisible zip foot from the top down.The foot has two grooves; the coil runs in one of them, held uncurled, and the needle drops immediately beside it. Sew from the top of the zip down as far as the slider will let you go, then stop and backstitch.
7. Do the second side, checking the two sides align.Close the zip and mark across both tapes at a couple of points — a waist seam, a horizontal stripe — so the two sides will line up when closed. Then open it, pin the second side face down on the other garment piece, and sew from the top down again.
8. Close the seam below the zip last.Fit an ordinary zip foot. Start about 1cm above where the zip stitching ended, sewing over the previous stitching for that overlap, then continue down the seam. Beginning below the zip stitching leaves a visible bubble at the zip end.
9. Catch the loose tape ends down.The bottom few centimetres of tape hang free inside. Stitch them to the seam allowance only — not through to the garment — so they do not flap.
10. Press and check.Press the seam from the wrong side with a cloth. From the right side you should see a plain seam line with only the slider showing at the top.

Tips

• If you have no invisible zip foot, a regular zip foot can be used with the coil held back by hand, but it is genuinely difficult and the results are usually visible. The proper foot is inexpensive and universal fittings exist for most machines.
• Sew both sides in the same direction — top to bottom — even though it feels natural to reverse for the second side. Sewing in opposite directions makes the two sides hang differently.
• A zip that shows on the right side after all was stitched too far from the coil. It is a one-millimetre problem.
• If the slider will not pass after sewing, the stitching is too close. Unpick a centimetre at a time from the top until it runs.

Common mistakes

• Sewing the seam before the zip — There is then no way to lay the tape flat under the foot up against the coil, which is the only way an invisible zip goes in invisibly. Unpicking the seam is the only recovery.
• Not pressing the coil flat — The foot cannot hold a tightly curled coil in its groove, so the needle ends up too far from the teeth and the zip shows.
• Using a zip cut to the exact opening length — The slider has to move above the top of the opening while you sew each side. Buy long and leave the excess in the seam.
• Starting the seam below the zip stitching — It leaves a small unstitched gap and a bubble right at the base of the zip, which is exactly where the eye goes.

If it doesn't work

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