To make one, I will assume you have a bra pattern that fits already. You need the upper and lower cup and you will cut them out of sheet foam, also called pre-finished padding, or poly-laminate foam. The foam is chlorine resistant and really easy to use.
Mark 1/4" (6 mm) away from the cross cup seam only. That's the one at the bottom of the upper cup and the top of the lower cup as shown here
Cut away the seam allowance
Set the machine to a zig-zag stitch (approximately 6 mm wide and 1.5 mm long). Butt the two edges of the cross cup seam together and stitch, easing them together as you stitch.
With a bit of luck, the two ends will match up perfectly. Sometimes you can make it happen!
Make three of these forms, exactly the same way. Pick one of them to be the outside layer, so that one needs the elastic allowances trimmed from the edges. The prosthesis needs to fit inside the finished bra cup so you can trim off at least 1/2" (12 mm) from the perimeter. Mark the outside edges of the cup and trim them off.
Each layer will be cut smaller than the one before it, and each layer will be smaller by at least 1/2" (12 mm). A lot of these numbers will depend on the size of the cup, but this is a good guideline to follow. You may need three layers - more if you want a lighter weight cup, and less if you want a heavier cup.
Now you need to weight the smallest of the cups you made. But first, you need to make a back for it to hold the weights. Lay the smallest cup on the foam and trace the footprint. Cut it out.
Zig-zag the edges of the back to the cup, but leave an opening to fill it along the top edge.
Fill the smallest cup with poly pellets. These pellets are commonly used in weighting stuffed toys or teddy bears, and are available at Michael's ($15) or in Ontario at Len's Mills ($5). They are inert, chlorine proof, washable and best of all, inexpensive. The form I am making is going inside a 42C Classic Bra. To start with, I used one cup of pellets.
I pinned across the top and assembled the cup to try it in the bra and on the student.
You can judge the weight fairly easily...just add or take away until your model says the weight feels right! She is the best judge of the weight and firmness.
I took out pellets from the small cup as my model felt it was a bit too firm and did not pass the "hug test". Women will judge the success of the prosthesis if, when hugged, no one can tell the difference between the two sides. I ended up using only one-half cup of pellets (I started with one cup)
I also noticed that we needed some building up in the top of the cup. Generally speaking, you want the weight toward the bottom of the cup, not the top. Since I had removed some pellets, I filled in the space with some foam scraps.and hand stitched them in place.
The layered cups from the inside. You can see the three layers quite clearly. If they need to be hand tacked to keep them from shifting, do that now.
Lastly, you need to make the back for the outside (largest) layer. Once again, trace the footprint of the largest cup.
Zig-zag it all around the cup. The breast form is finished!
Here it is from the front
Here it is in the bra. The form fits inside the bra cup and the pocket, a piece of fabric that sits against the chest wall, that holds the form from shifting around or falling out. Think of a pocket bra as being a pillow sham. The pillow (the breast form) fits through the opening in the pillow sham (the pocket).
Many thanks to our student in Boob Camp who happily modeled this bra for the picture! Yes, she really did have a mastectomy - although it is difficult to tell which is the natural and which is the do-it-yourself form. The total cost of this form was less than $10 (0.50 for the pellets and $7.50 for the foam). It took me a couple of hours in total to make the form (but I was taking photos along the way!)