Optional: If you would like to cover the zig-zag on the inside of the cup, you can cover the bottom cup seam with bias tape before joining to the upper cup, then cover the upper cup zig-zag seam with bias tape as well. OR, you can cut a layer of lining fabric to sandwich in the next step to cover the foam.
Next, attach the upper cup using the same method with the zigzag stitch. Be sure to align your notches. When assembling, respect the curve of this seam and your cup should begin to take shape as you are attaching the top cup this way. With the right side of your self-fabric cup facing the wrong side of your foam cup liner, attach along the top edge with a 1/8" straight stitch. Elongate your stitch at least .5 as this will be a very tight stitch and the density of the foam can cause tension issues and skew the 1/8" amount. It is vital to maintain that distance along the top edge. Removing your seam allowance on the foam cup liner allows for the self fabric to curve over the top edge and create a clean seam finished look. *Ignore the paint on my hands! I have been painting my new studio recently and I have the battle scars to prove it lol.