It is always best to reinforce the shoulder seams of knit (stretchy) garments to prevent them from losing shape. Below are four of several methods that can be used to reinforce shoulder seams. All shoulder seams in this tutorial are reinforced on the wrong side of the back bodice.
Cotton tape reinforced seam.
I used 6 mm (¼ in) wide cotton tape for this tutorial because it is thin, soft, and not at all bulky. It is best to preshrink a length of cotton tape before applying it to a seam.
Cut the cotton tape the length of the shoulder seam and place it over the seamline, just below the seam allowance edge. Tack or pin the tape in place. Stitch it in place with the tape side up using overlocking or a zigzag stitch and avoid trimming the tape as you sew.
Press the seam allowance towards the back bodice.
Self-fabric reinforced seam.
It is best to use thin knits that stretch slightly lengthwise for this method. Cut a 2 cm (¾ in) strip of self-fabric on the lengthwise grain. Place the strip of self-fabric over the shoulder seamline and tack or pin it in place. Stitch the shoulder seam using overlocking or a zigzag stitch. Trim the excess fabric close to the stitches. Press the seam allowance towards the back bodice.
Fusible knit interfacing reinforced seam.
Cut a 1 cm (⅜ in) wide strip of fusible knit interfacing the length of the shoulder seam. Fuse it to the back shoulder seam. Stitch the seam using overlocking or a zigzag stitch. Press the seam allowance towards the back bodice.
Clear elastic-reinforced seam.
Cut a length of 6 mm (¼ in) wide clear elastic and secure it on the back shoulder seamline. Stitch the elastic to the shoulder seam using overlocking or a zigzag stitch and avoid trimming the elastic as you sew. Press the seam allowance towards the back bodice.
