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.