How to Sew In a Zipper. There may come a time when you need to add or replace a zipper to an item or article of clothing to add or restore function. It's easy to sew a zipper into most fabrics if you have a little knowledge and the right equipment. Here's how to sew a hidden zipper into any straight seam, which is great for applications such as a bag, pillowcase or clothing.
Measure the seam you would like to sew the zipper into. Use a seamstress tape and a flat surface to get the most accurate measurement. Buy a zipper for your weight fabric in a labeled length at least as long as your measurement in a matching or coordinating color.
Sew a basting stitch in the seam and press it open. Pin your zipper to the wrong side of the fabric. Center the teeth in your basting line and pin the zipper tape selvages beyond the opening.
Make a straight stitch around the outside of the pinned-in zipper with a zipper foot. Keep your stitching line as close to the zipper's teeth as possible.
Reinforce the top and bottom by back-stitching across a few times. This will keep the zipper pull from going beyond the opening of the fabric.
Pull out the basting stitches gently with a seam ripper. This will open up the seam and make the zipper functional. Don't go beyond the reinforced ends of the sewed-in zipper.