One of the frequently expressed complaints that women have about swimsuits, both handmade and ready-to-wear, is that they don’t offer enough bust support. There are two easy ways you can add bust support to your swimsuit – by adding boning and/or cups. Even those of us that aren’t busty enough to require extra support can enjoy the benefits of boning and cups for they also help a swimsuit stay in place and hold its shape.
Boning: Boning offers a little bit of support and helps a swimsuit (especially a bikini top) to keep its shape. It can be inserted into just about any swimsuit as you are constructing it – all you need is a side seam. After you sew the side seam, sew another seam 1/4″ from the side seam to create a vertical channel. Insert a piece of plastic boning (that you have cut to size and rounded the ends) into the channel. Remember that your boning will need to be shorter than the unfinished channel length because you still need to sew elastic to the top and bottom. [To see an example of boning insertion in a step-by-step tutorial, you can check out the Sewalong for my Nautilus Swimsuit Top.]
If you want to add boning to a one-piece suit, you will still want to make the boning the same length as if it were for a bikini (5″ is a good ballpark). Sew a channel in the same manner, but close off the bottom of the channel ~5″ down with a line of horizontal stitches across the channel.
If you want to add boning to a ready-to-wear swimsuit, sew a strip of swimsuit lining to the inside of the suit at the side seam, insert the boning, and then stitch across the top and bottom of the channel. Alternatively, sew the channel seam, cut a small slit through the lining at the top of the channel, insert the boning, and sew the slit closed.
Bra Cups: Inserting cups into a swimsuit as you sew it is as simple as sliding purchased swimsuit cups between the suit fabric and lining as you construct the suit. Depending on the construction of the suit, the cups may stay in place on their own or you may need to tack them in place from the inside. Before tacking them in place, try on the finished suit, position the cups where they best fit your individual body, pin them in place, and then remove the suit and tack them down. [For more information on choosing cups see the post on my blog about How to Insert Bra Cups Into a Swimsuit.]
To insert cups into a ready-to-wear swimsuit, you can cut a small slit in the lining fabric, slide the cups in, and tack them in the same manner. You can sew the slit closed or just leave it as the lining fabric will not unravel.
If you can’t find swimsuit cups that fit you or you want the extra support of an underwire, consider sacrificing an old (but well-fitting) bra instead. Cut your bra in half and remove the straps. Cut a piece of swimsuit lining, cut an X in the center (the size of the X will depend upon your cup size), push the cup through, and pin the cup into place.
Sew the lining to the cups, being careful not to hit your underwire and use the lining piece in your normal swimsuit construction. You can machine sew through the cup itself or hand sew around the edge of cup.
To prevent visible lines from the front, you may want to cut away the excess lining fabric. If you want a pretty interior finish, you can cut a second piece of lining and use it on the inside of the sewn-in cups. [Thanks so much to Elaine for the idea and photos of inserting a bra into her swimsuit. Read her mini-tutorial on Curvy Sewing Collective for more.]
Alternatively, use your chopped-apart bra just like you would a purchased swimsuit cup – insert it between layers as you sew and tack it in place as described above.
*A bit of self-promotion: check out my Nautilus Swimsuit for a swimsuit pattern with multiple cup size options that includes instructions for both boning and cup insertion.*