I have heard from a few Fenway bra makers that their fold over elastic does not have a very firm stretch. If this is the case for you, there is a simple solution! I use this same method when I want to use a decorative trim that is technically just a bit too stretchy for bra making.
In addition to your elastic trim you will need clear rubber elastic. Clear elastic is thin and smooth so it does not add bulk while adding strength and elasticity to the area.
The width of the clear elastic you use should be nearly equal to the finished width of your trim. In the case of fold over elastic, this will be ½ of the total width of the elastic and for other trims, make sure the width of clear elastic will be covered by the trim.
In the case of fold over elastic, when you are ready to apply your elastic, start by zigzag stitching the clear elastic to the bra along the bra edge on the wrong side of the bra. If necessary, use a 3-step zigzag stitch to prevent tunneling of the fabric and elastic. Follow by applying the fold over elastic as directed.
If you are using trim that needs some extra firmness, the method of application is determined by the area of application. Just keep in mind that you want to be sure the clear elastic is not positioned on top of any plush elastic and that it is not visible from the right side of the fabric.
For the standard two-step elastic application process used in my bra sewing patterns, you can sandwich the clear elastic between the right side of the garment and the lingerie elastic and apply the lingerie elastic as usual.
Don’t you just love all the options you have when making your own bras?!