Invisible or concealed zips are hidden within a seam. The only part that can be seen from the outside is the zip slide, giving garments a neat, professional look. They are nylon coil zips with the coil on the back of the zip rather than the front so its teeth are hidden behind the tape. They’re the easiest zip to insert as you long as you work carefully.
Where are they used?
Invisible zips are commonly used in skirts and dresses where you don’t want the zip to show and need a smooth, neat finish. They also work well on cushion covers for a seamless look. It’s best not to use them for thicker fabrics or items which will have a lot of strain as they could break if put under too much pressure. They should be sewn into a seam before you sew the seam above or below it as you’ll get a neater result and it will be easier to insert the zip when the fabric is flat.
Which foot to use
Invisible zips are attached in a different way to standard zips and are sewn onto the right side of the fabric. It’s best to use a special invisible zip foot. These have two small grooves at the bottom for slotting the zip teeth into as you stitch. Make sure you buy one that fits your sewing machine brand and model as they do vary.
If you don’t have an invisible zip foot then you can use an ordinary zip foot instead using this method, but don’t use a general purpose foot as you won’t be able to get close enough to the zip teeth and the foot will get in the way. Prepare your fabric, tack the zip into place and press the teeth flat as explained below. Lower your foot on the zip tape as close to the teeth as you can then swing the needle over so it goes into the zip tape right next to the teeth. Stitch the zip in place, making sure you keep the teeth rolled over and the needle up close to the teeth.
Buying a zip
There are different weights, lengths and colours of invisible zips available to buy – just choose one in a colour to match your fabric and a little longer than the seam you want to sew it into for a neat finish at the bottom.
Lightweight and transparent nylon concealed zips are available, which you can use for sheer and lightweight fabrics. Invisible zips can be bought from most craft and haberdashery shops or online.
If you are inserting a zip into a lightweight or stretch fabric then press a narrow strip of iron-on interfacing to the wrong side of the seam allowance only. This won’t be seen from the front but will stabilise the fabric and stop the seams from puckering as you stitch.
If your garment isn’t going to be lined or the fabric frays a lot then it’s best to finish the edges of the seam allowance that the zip is going to be stitched to with a zigzag stitch.
Positioning the zip
It’s really important to get the placement of the zip correct so that the teeth lie just beneath the seam allowance and are hidden from the front. There are several methods of doing this and everyone has their preferred one. Most people pin one side of the zip tape in place then stitch it on, then repeat on the other side. Using the method of stitching the seam first before you pin and tack then unpicking it does take a little longer but ensures a neat placement. It’s important that the zip matches at the top and that any horizontal seams that the zip passes through, such as waistline seams, match up perfectly when the zip is done up.
Inserting an invisible zip
Pin the two pieces of fabric that the zip will be inserted between with right sides (RS) together.
Using a long machine stitch, stitch these together along the seam allowance given for your pattern.
Press the seam open – do this carefully as it’s not as stable as a normal seam.
Keeping the fabric wrong side (WS) up place the zip (zipped up) centrally on top RS down. The teeth should lie exactly on top of the seam with the zip slider in the position you want it to be when finished.
Now tack it into place so that it’s really secure when you machine stitch it – you should only tack it to the turned over seam allowance and not into the main fabric. Only tack down to the end of the long stitched seam. A little of the zip will reach beyond this as this gives a neater finish.
Undo the long machine stitching you worked earlier. Your zip is now positioned in exactly the place you want it to be and both sides will match up when stitched in place.
Uncurling the zip
Undo the zip right to the bottom then roll the teeth over and press the WS of them so they lie flat. Use a warm, dry iron for this so you don’t melt them. This will help when you stitch the zip in later.
Stitching one side in place
Open out the fabric so it is RS up. The zip will be RS down on top with the seam allowance folded out flat, the zip tape near the edge of the seam allowance and the zip teeth on top of the pressed-under allowance.
Swap your general purpose foot for an invisible zip foot (if you don’t have one, see above for working with a zip foot). Starting at the top of the zip on the left side of the fabric seam, slot the teeth of the zip into the right groove of your invisible foot. Your needle will go into the zip tape and fabric just to the left of the zip teeth.
Reverse stitch to start then stitch all the way down the zip, making sure that the teeth stay under the groove on the foot. Stitch until you reach the end of your tacking stitches so there is a little of the untacked zip beyond.
Reverse stitch to secure the seam.
Stitching the other side in place
Stitch the other side of the zip in place in exactly the same way starting at the top and stitching down to the bottom of your tacking stitches. Make sure the fabric and seam allowance is lying flat.
The teeth should lie under the left groove of the foot this time and the needle will go into the zip tape and fabric just to the right of the zip teeth. Pull up the slider to do up the zip.
Stitching the seam below
Swap to an ordinary zip foot in your machine. Pin the fabric RS together starting right at the bottom of the zip and finishing at the end of the seam.
Hold the loose unstitched part of the zip out of the way and start stitching the seam about 2cm (¾in) up from the bottom of the stitching you worked to insert the zip. You won’t be able to stitch right on top of this as the teeth will be in the way, so stitch as close as possible without catching the zip tape or teeth. This is a little fiddly as the zip is in the way. Work slowly, remembering to reverse stitch so the end of the seam is secure.
Continue stitching the seam using the seam allowance detailed in your pattern.
You’ve now finished, but for neatness hand stitch the bottom ends of the zip tape to the seam allowance to keep them laying down flat. Don’t stitch through to the front.
At the top of the zip, your pattern should tell you how this is finished as it can be folded over at the top and tacked to the seam allowance or sewn into the facing, depending on the type of garment.
From the RS press your seam and zip edges flat, remembering to take care when pressing the zip so you don’t melt it by using a cool iron for this.