Lycra is DuPont's trade name for spandex, a stretchable, synthetic fibre. Lycra fabric is available in either two-way or four-way stretch and used for swimming costumes, sportswear, intimate apparel and costumes. Fabric manufacturers add Lycra fibres to fabrics to provide elasticity and help garments to maintain their shape. Shiny leotards are made of Lycra blended with nylon, but workout apparel is usually matt because the Lycra is blended with cotton. Sewing Lycra fabric requires preparation because of its instability. With a few tips, though, you can sew seams that are both flexible and strong.
Change the sewing machine's regular needle to a size 70/10 ballpoint needle. That needle is blunt and pushes the Lycra fibres aside instead of tearing them. Use polyester thread because it provides more elasticity in seams than cotton thread.
Adjust sewing machine settings. Set the sewing machine to 5 to 6 stiches per cm (12 to 15 stitches per inch), and turn the machine's tension knob to a lower number.
Practice sewing on scrap Lycra fabric. Use either a straight or small zigzag stitch, and stretch the fabric as you sew by holding the fabric both in front of and behind the needle. Test the different stitch lengths and the tension setting on scrap fabric to ensure that the fabric does not pucker while you sew. Adjust them if necessary. The editors of "Vogue Sewing" wrote to "test the stitching on both the lengthwise and crosswise grain before you begin your garment."
Pin your project together to prepare it for sewing. Put straight pins into the fabric perpendicular to the fabric's edge and only in the seam allowance.
Sew the seam slowly with even pressure on the sewing machine foot pedal.
Remove each pin just before it reaches the presser foot. This will help to prevent mistakes. Needle holes in Lycra are permanent and visible.
Sew a parallel line of either straight or zigzag stitching in the seam allowance 3 mm (1/8 inch) away from the original line of stitches.
Trim the seam 3 mm (1/8 inch) away from the second set of stitches.
You can save time by using a serger, which cuts and finishes the edges as you sew. Thread appears lighter when it's sewn. So use a thread that is one shade darker than your fabric.