In this tutorial I have photographed a few of the steps from the Jazz One piece and bikini patterns.

Wadding

This pattern uses Bra wadding.

Bra wadding / spacer is sewn inside the cups to add support.

This is Laminated Foam; it can be purchased from fabric shops and lingerie suppliers.

Wadding is often used in swimwear, it is a very handy fabric to have in your sewing stash.

It is easy to use and adds professional appearance to your swimsuit.

Sewing tip Add lining to Outer front cup sections.

This is a great tip which prevents the any ridges from the wadding seam showing through.

Stitch Centre front seam

I have photographed the top section at this point so you can sew all of the steps completed so far.

Sewing tip Stitch centre front casing for the detachable strap style.

This is the easiest version of the 3 options this pattern includes.

If you are a little overwhelmed by this pattern, I highly recommend you choose the Detachable straps style to sew first.

How to Stitch wadding sections to create cups for Jazz One piece & bikini pattern

The Jazz patterns use Wadding or Spacer in the bra sections. This is a foam fabric which is also used in premade cups.

Its approximately 3mm or 1/8 inch thick. It is available in fabric shops & Bra lingerie supply shops

In this step, you will stitch the top & lower wadding sections of cups together.

Set your machine to a wide zig zag stitch.

Stitch top to lower section of each cup by placing the seam edges together, as shown. Do not overlap.

Match circle dots as you stitch the wadding sections together.

Completed cups. You can use other wide stitches also. A cover stitch will also work on this step.

Sewing tip Add lining to the outer cup sections to achieve a smoother appearance.

How to line the outer cup sections to achieve a smoother appearance.
The sewing instructions -read to Cut 2 of the Outer cup sections.
Here we are recommending you also Cut 2 of the Outer cup pattern piece from the lining fabric.

This lining layer will be sandwiched between the Outer Cup section & the wadding sections at a later step. The lining will help prevent seeing ridges from the wadding seam.

This is often more visible in light coloured fabrics & prints.

How to sew the centre front sections together.Detachable straps version.

At this point The binding is sewn to the top edges & I have attached the loops using bra casing tape for the detachable straps.
As you can see the excess binding on the back section is curling up, I will trim that later.
I also stitched the lycra strip over the cup seams using my cover stitch machine. This is an option in the sewing instructions, I also recommend you complete.

Stitch the centre front sections right sides together. Seam allowance 3cm / 1 1/4 inches.
As you sew the centre fronts together, Stitch just on the very edge of the centre front wadding. You can use a straight stitch here.
This sewing pattern includes 3 style options.
Detachable shoulder straps, Centre straps & V-wire style.

I have sewn the simplest version -Detachable straps version.

The V -wire & Centre straps versions require a casing seam that is formed from the wide seam allowance.

The pattern includes sewing instructions to guide you through each of those versions.

Open Centre front seam.
Stitch a long/gather 2cm or 3/4 inch from centre front seam, on each side of seam allowance as shown.
Draw in the stitching row to tighten the outer edges of the seam allowance.
Press the seam open.
In the next step, the instructions inform you to stitch the seam allowance to the top section on each side to create a casing.
Stitch centre seam allowance 2cm or 3/4 inch on each side of centre seam. Stitch through all layers.

There is no need for a casing in the detachable straps version.
I would prefer not to see this stitch line on the outer front side of the swim suit.
Instead of stitching through all layers, you can stitch the seam allowance to the wadding layer only.
How to
Flip the outer front section up, Stitch the seam allowance to the wadding only on each side of the centre front seam. Stitch from top to lower edge 2cm / 3/4 from centre front seam.Trim excess edges. Fold outer front section down.

Continue to follow sewing instructions of Jazz one piece or High waist Jazz bikini pattern.