Sometimes leotards and swimsuits are so thin that you wish they had a lining. So, here is how you can hand-sew a layer of lining into garments made of stretchy fabric, such as spandex (also known as elastane or Lycra).
(Note: Please click on the photos to enlarge them for a close-up view of their detail.)
1. As shown in the photo, prepare a sheet of spandex that is a bit larger than the section of the leotard or swimsuit you wish to line. It is important that the section be bordered by existing machine-made stitching as you will sew through those seams to hide your new stitches. (In the photos I will show the process of adding a lining to the entire front section of a leotard.)
Turn the garment inside out and place it on top of the fabric, with the section of the garment you wish to line against the fabric. Center the section to line on the lining fabric.
2. Carefully turn over both items (at the same time) so that the fabric lining is on top.
Flatten the fabric against the garment, and carefully pin the fabric along the outline of the section you wish to line. (Do not stretch the fabric; just straighten it so it does not get twisted.)
3. Before you begin to sew, please note the following:
Use regular polyester sewing thread for the sewing (in a color which matches the thread of the garment’s seams).
Do not cut out the lining yet, but sew over the fabric as shown in the first photo on the left; you will trim the lining after you sew it onto the leotard or swimsuit.
Sew along the existing machine-made seams of the leotard or swimsuit, but make sure that the stitches are at least 3 mm (1/8″) away from the outer edges of the seam. (Note: The second photo on the left was taken after the lining was trimmed to show the gap that should be at least 3 mm (1/8″).)
4. To sew the lining onto the garment, use the Catch Stitch, with a knot in every fourth stitch to make the seam stretchy!
Here is how:
In the drawing, the garment is shown in pink, the patterned band is the existing machine-made seam of the garment and the green is the lining layer on top. (I made the lining partially transparent in the image so that you can see where to sew.)
Starting at one end of the section your wish to line, for example the crotch of the leotard or swimsuit, make 4 zig zag stitches: A-B, C-D, E-F and G-H.
5. Now stretch the fabric of the stitched area so that the thread in the stitches becomes a bit loose.
6. Without making the loosened stitches taut again, make a knot very close to the fabric on the lining side, as shown in red in the drawing.
7. Repeating steps 4 through 6, continue to work your way up along the outline of the garment by section. For example, sew both sides of the torso, then the arm holes, the top of the straps, and finally the neck line. (Sewing by section on both sides of the garment will help to keep the lining nicely aligned with the garment.)
8. When you have finished sewing the entire outline of the section of the leotard or swimsuit you wish to line, cut the lining fabric along the hand-stitches.
You need to cut very close to the hand-stitches, but be careful not to cut the stitches or the garment fabric! Trim enough so that its edges of the lining remain hidden on the inside of the leotard or swimsuit.
10. When you flip the leotard/swimsuit right side out, the newly attached lining, as well as your stitches, should remain hidden from view!
Now you are ready to go swimming or dancing without feeling uncomfortable about what you are wearing!