Things You'll Need
Sewing machine (with zigzag and stretch stitches)
When you sew with spandex, you face the challenge of working with fabric that has a two-way stretch, both lengthwise and crosswise on the grain of the fabric. Because of this special stretching quality of spandex fabric, you must take care not to stretch it out of shape as you sew it. To sew a hem in spandex fabric, finish the raw edge of the fabric first to prevent unraveling and then sew a narrow hem in place with the sewing machine.
Set the sewing machine to stitch a medium-width zigzag stitch along the raw edge of the spandex. Place the spandex fabric into your sewing machine and zigzag the raw edge of the spandex to prevent it from unraveling.
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Determine the hem you desire and turn the fabric to the wrong side along this line. Pin the hem in place to hold it securely.
Set the sewing machine to a stretch stitch. A stretch stitch works well for sewing stretchy fabric because your machine will stitch two forward stitches and then one backward stitch, creating a stitch that will stretch with the stretch of the spandex. Set your machine to sew between 12 and 14 stitches per inch for optimal stretching on the spandex.
Place the spandex fabric into the sewing machine with the wrong side facing up so you can see the zigzagged edge of the pinned fabric. Position your needle to sew along the fabric approximately 1/4 inch from the fabric's edge.
Sew the stretch stitch along the fabric to hem the spandex. As you sew the stretch stitch, expect the sewing process to take longer than usual because your sewing machine will be stitching two forward stitches and then one backward stitch along the entire hemline. Sew slowly and carefully to finish the hem.
Remove the fabric from your sewing machine and clip the threads. Remove the pins to finish.
If you have a serger, use the serger to stitch the raw edge of the spandex instead of sewing a zigzag stitch with the sewing machine. Proceed with the remaining hemming steps after serging the raw edge of the spandex.
If you have a blind hem foot for your sewing machine, you can sew a blind hem after finishing the raw edge of the spandex. A blind hem will not be visible from the right side of the spandex.
If your sewing machine doesn't have a stretch stitch function, you can still hem spandex and other stretch fabrics using a straight stitch, either with a twin needle or by gently stretching the fabric. A narrow zigzag stitch is also effective.
A walking foot can be very useful for sewing stretch fabrics.