How to Add Breast Support to a Swimsuit (Sewing a Bra Tips)

For many women, the lack of bust support in off-the hanger swimsuits is a constant source of frustration. No matter how lovely the suit, a lack of support in the crucial area can let you, and the suit, down.

Fortunately, a little trickery and a few basic sewing skills might be all you need to transform your swimsuit… and your figure with it. Adding boning, underwiring, and/ or cups can be done easily enough, and doesn’t require any special skills or mastery with a needle. That said, it pays to do a little research into the different possibilities before you get down to business.

How to Add Support to a Swimsuit


While some options will do great things for your shape (and after all, even if you don’t technically require much by way of extra support, who can say no to a little extra shape and a more flattering silhouette?), others are better for providing support (thereby being a must-try for ladies with a fuller-figure).

Whether you're in the market for full coverage and as much support as possible, or are looking for just a little extra modesty and an enhanced shape, you're in the right place to find out how to get it. (related article: one-piece swimsuit too small)

How to Add Boning to a Swimsuit

If you’re looking for a little support and a lot of shape, boning is your surest fire of getting it. As long as your swimsuit pattern has a side seam, boning can be added simply and easily.

Adding Boning to a Bikini top Pattern

Make the top as per the pattern. Once you’ve sewn the side seam, sew a second seam of the same length about ¼ inch away from the first. Cut a piece of plastic boning just a little shorter than the vertical channel you’ve sewn and round of its ends. Insert the boning into the channel before continuing with the rest of your pattern.

Adding Boning to a One-Piece Pattern

Follow the same steps as above, but after you’ve stitched the channel, close off its bottom edge with a series of horizontal stitches.

Adding Boning to a Rady-to-Wear Swimsuit

Cut a thin strip of swimsuit lining and sew it to the inside of the suit at the side seam to create a lining “tube”. Insert the boning and close of the lining at both ends.

Adding Underwire to a Bathing Suit

If you want to make sure your swimsuit has plenty of support, underwiring is one of the best ways of going about it. The following method is relatively simple and works with just about any swimsuit pattern. If you struggle to find any of the necessary elements at a fabric store, you’ll find them widely available online.

What You’ll Need

  • Power Net
  • A Set of Underwires
  • ​Bra Channeling
  • Fabric Pen

The Method

  • Take the power net and cut out a front and back bodice. Mark the center front on the wrong side of the net.
  • Cut the channeling to measure 1 inch longer than the underwiring.
  • ​With a fabric pen, trace out the shape of the underwire onto the power net. Place the wire ½ inch from the center front line and around 1 inch from the lower edge.
  • ​Draw out from the existing lines by about ¼ inch on the side closest to the center, and by about ½ inch on the other side (the result should be proportionate to your bust size: if you have a larger bust, you may need to angle the lines out a little further).
  • ​Baste the channeling in place along the line, leaving a ½ inch free-floating above each side.
  • ​Insert the underwiring into the channeling. If one side of the wiring has a colored tip, feed it through the basting so that the colored tip is closest to the front center. Take care to feed the wire through the channeling itself, rather than in the gap between the power net and the channeling.
  • ​Sew the side seam of the swimsuit and try it on to check for fit. The wire should be flush against your body and sit just below your bust.
  • ​If the underwiring fits well, remove the wire from the channeling and stitch the sides to secure the edges. Stitch a bar tack over the ends of the channeling to close the center front edges.
  • ​Repeat the same process with the other wire. Trim the channeling as close to your stitching line as possible.
  • Run the wire through the channeling and close the opposite side of the channeling using the same method as previous.

How to Put an Underwired Bra in a Bathing Suit


If you want the extra support of underwire but don’t want to go to the effort involved in the previous method (or if you’re looking to add it to a ready to wear piece, rather than a swimsuit you’re making yourself), there’s an easy alternative.

The Method

  • Take an underwired bra and cut it in half through the center. Remove any straps and embellishments.
  • Cut 2 ‘X’ shapes through the front lining of the swimsuit where you want the bra cups to sit (bear in mind the size of the X’s will be relative to your bust size). Push the bra cups through, and pin in place.
  • ​Sew the lining of the swimsuit to the cups, taking care not to sew over the underwiring.
  • Cut away any excess lining fabric to finish.

How to Sew a Bra in a Swimsuit


If you want full-blown support and a good amount of coverage, sewing a bra into your swimsuit is a great idea. Simply take any old bra from your closet (although you’ll probably want to make sure it’s one that offers a good degree of support and comfort. If it has a foam padding, you might want to test whether it’s water-resistant first, otherwise, you risk having to wring yourself out after each dip), then grab your sewing supplies and follow this super-easy guide.

The Method

  • Complete the swimsuit as per your pattern, but stop just at the point that the front and back are attached, but you haven’t yet added the straps. Using a serger or zig-zag stitch, sew the fashion material to the lining along the top to form one piece.
  • Cut the strap at the back of the bra band and above the cups. If the bra has any embellishments that might affect the smooth line of the swimsuit, trim them away.
  • ​Lay the bra over the front of the swimsuit, skin side out. If the bra has underwiring, position the bra so that the underwire is at least ½ inch or more below the neckline. Pin to secure in place. If the cups are fuller than the suit, you may need to add a few darts to ensure a smooth finish.
  • ​Using a narrow zig-zag stitch, sew along the neckline, leaving the back of the bra free-floating.
  • ​Trim any excess to ensure the bra can’t be seen above the neckline of the swimsuit.
  • Bra part now finished, you can continue with the rest of your pattern.

Sewing Cups Into a Bathing Suit


Sewing cups into a bathing suit is one of the simplest ways of adding extra comfort and support. All you’ll need to get started are basic sewing supplies and some bra cups.

As the method depends on whether you’ll be adding the cups to a ready-to-wear swimsuit or one you’re making yourself, be sure to note the slight differences between the following guides (although for both methods, the prep stays the same).


Choosing the Right Cups: Most fabric and craft stores carry a good selection of bra cups. If you want to save a few dollars, it’s worth hitting your local thrift store for a swimsuit you can scavenge the existing cups from.

If you’re adding cups more for modesty than for support, a soft cup will do the job well enough. If you want the best of both worlds, look for a foam cup (although before you install it into your swimsuit, make sure it won’t soak up water like a sponge the second you hit the pool). If you can find a pair of seamless, lightweight and water-resistant cups (some will even be labeled ‘for swimwear’), so much the better.

Choosing the Right Size Cups: Unlike with bras where buying the right size is an exacting science, you can afford to be a little more casual with swimsuit bra cup sizes. You’ll find cups often cut across measurements (A/B, B/C, etc.). As a general recommendation, going slightly larger than your usual size tends to be the best way of keeping the cups firmly in place; if you’re usually a B cup, plump for the B/C size instead of the A/B, and so on.

Sewing Bra Cups Into Ready-to-Wear Swimsuits

  • Cut a small slit in the lining of the swimsuit.
  • Insert the cups through the slits and pin them in place.
  • ​Try the suit on (being careful to avoid the pins) and make any adjustments necessary to get the fit just right. Add a few more pins to secure.
  • Sew the cups in place, starting at the bottom of the edge cup and working your way around the edges.

Sewing Bra Cups Into Swimsuit Patterns


Simply slip the cups between the suit fabric and the lining as you make the suit. Some suits will be constructed in such a way that the cups will naturally stay in place; others might need a helping hand. Once you’ve added the cups, try the suit on and check how the cups fit. If you feel they need some extra stability, pin the cups in place, remove the suit, and tack them in place.

How to Increase Modesty Without Support

If you want modesty but don’t need the support of an actual cup, simply cut out several layers of lining fabric, stitch them together to create one piece, and sew in place along the inner front of your bathing suit. For smaller chested ladies, this is a quick way of making sure you keep your modesty after a dip, without getting the bulk or unnecessary support of cups.

Sewing With Swimsuit Material

Whether you’re adding cups, bras, boning, pads, or anything else to your swimsuit, it pays to know how to work with swimsuit fabric. Even for the most experienced crafter, sewing with swimsuit fabric (or really, any kind of material that’s designed to put the 'streeeetch' in stretch) can be challenging. Fortunately, it doesn’t have to be. Follow a few top tips, and your days of fearing Lycra will soon be over.

Choose Your Fabric Wisely


Swimsuit material tends to come in one of two types: ones with a 2-way stretch and ones with a 4-way stretch. 2-way stretch fabric stretches horizontally only. 4-way stretch fabric stretches both horizontally and vertically, meaning it will stretch just as well around the body as it will up and down it. Make sure that the fabric you choose is appropriate for your pattern to avoid a disappointing result (not to mention a tougher sewing experience than’s necessary).

Use the Right Equipment

If you’re working with stretch materials, you’ll want to make sure your equipment is up to the challenge. Don’t be tempted to use anything but stretch needles, and always opt for a polyester thread over cotton.

Choose The Right Stitch

If you’re basting or attaching elastic to the swimsuit fabric, a classic zig-zag stitch or triple zig-zag stitch both works well. If you need a straight line of stitches, opt for the triple straight stitch, the stretch stitch, or the lightning stitch.

Practice Makes Perfect

If you’re new to sewing with stretch fabric, get your nerves out of the way before tackling the swimsuit by testing different stitching types and methods on a patch of spare material. Try folding the fabric in half to see how it feels working with layers, and even practice a few seams. By the time you start on the swimsuit, you’re guaranteed to be feeling much more confident.

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