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Sandwich 2 layers of batting together and pin them. Use a sewing machine to straight stitch around the edges of the stack. Mark 2 darts on the curved edge of the batting. Pin and machine sew the darts. Fold and pin the seam allowance of the lining fabric over the batting. Machine sew around the perimeter of the shoulder pads. Trim away the raw edges of the lining fabric.
Pair up the matching "R" and "L" pieces and pin them together. This will create a thicker shoulder pad that has 1 layer of batting. If you want your shoulder pads to have graduated thickness, cut out a series of progressively smaller pieces. Use fabric spray adhesive to secure the pieces together in a stack. You'll place another full-sized piece of batting over the top to smooth over the levels. Sew a straight stitch around the perimeter to hold the layers of batting together. The first dart will take in 14in (0.64cm) and the second, larger dart will take in 12in (1.3cm). The larger dart should go on the side with more volume which will be positioned towards the back of the shoulder. They can both be about 2in (5.1cm) deep. Mark these with a fabric marker or pencil. Pin in the darts on both shoulder pads, making sure you're taking in volume from both of the 2 layers of batting. Sew the darts closed using a machine straight stitch. Trim away the loose threads. Place the batting onto the wrong side of the corresponding "R" and "L" pieces of lining fabric. Position it in the center and begin folding the 1in (2.5cm) seam allowance toward the inside. Pin around the edges. The lining fabric should now be enclosing the edges of the batting. Take care in folding around the corners so that the seam allowance doesn't stick out or add too much bulk. Sew a straight stitch 14in (0.64cm) away from the folded edge. Now, your lining fabric should be totally enclosing all edges of the batting. Trim away the excess seam allowance. If you have pinking shears, use these when trimming away the seam allowance so that the raw edges of the lining fabric won't fray. Your shoulder pads are now ready to whip stitch into the garment of your choice!