Invisible or concealed zips create a more expensive ‘high end’ finish on garments. Where the opening for a zip is placed will have been considered when designing & marked on the pattern. There should be a minimum 1.5cm seam allowance for any seam with a zip fastening, fabrics that fray easily require a 2cm allowance.
Mark opening for zip, the top stop just above zip teeth is placed just below the seam allowance & the seam starts 3cm above the bottom stop where teeth end. Sew seam & press open.
Pull the runner as far down as it will go & lay the zip over the seam allowance, check right side of zip is facing down.
Pin the tape in place lining up the zip teeth with the 1.5cm seam allowance line. The horizontal pin in the image is level with the start of the seam.
Using a zipper foot on the machine stitch as close to the the zip teeth as possible, use your finger to roll the teeth back. Stop stitching level with the start of the seam (see blue chalk mark above).
At seam point stitch off the zip tape at an angle and back stitch to reinforce.
To sew the other side stitch in to the seam point & up. Pin first to make sure the two top stops above the teeth are level.
Avoid pressing directly onto the zip, gently run the tip of the iron along the wrong side of the garment fabric under the seam allowance & zip tape.
Garment Construction 