How to Sew a Swimsuit You'll Really Love

There are certain items in the closet that it seems like we never even consider making — bras, underwear, workout clothing, and swimsuits — but I’m thrilled that it seems as though many of us are breaking out of that mold and jumping into projects from all of those categories. No longer is sewing garments restricted to dresses, pants, skirts, and tops! More and more sewers are branching out into all of those unmentionables, including me. I’ve been sewing for over 30 years, and never once did I consider making my own swimsuit, until now.

When I saw the Bombshell Swimsuit by designer ClosetCaseFiles , I knew that it was the one for me, as it is very similar to a ready-to-wear suit I have worn and loved for many years. It’s a classic retro-style with three view options, all equally saucy, all incredibly flattering, especially to ladies with curves. This suit isn’t terribly hard to make, but there are a lot of steps — seeing them in clear photographs is helpful. It’s also really important to have the correct tools and materials on hand, or else the suit will not perform properly.

Because of the scope of this project, I have broken it down into two posts. In this, the first post, we will go from the very beginning to the halfway point where the front and back pieces are assembled. In the second post, we will spend our time putting the two halves together and finishing the suit.

Don’t get overwhelmed, simply take your time and do it in stages and before you know it, you’ll have a suit of your own! Please note that I am only making view A, though much of what is covered is applicable for views B and C as well.

What You Need

  • Bombshell Swimsuit pattern
  • Fabric and lining*
  • Elastic: This must be rubber elastic, not cotton or polyester, as it needs to hold up to saltwater and chlorine
  • Thread: Much like the elastic, this must be polyester thread, not cotton or any other fiber
  • Swimwear bra cups (optional)
  • Scissors
  • Rotary cutter (optional)
  • Water soluble pen
  • Clear ruler
  • Tape
  • Sewing machine needles: Stretch needles in size 90/14
  • Pins: Ball point pins for stretch fabrics
  • Pattern weights (optional)

*Note: Both the fabric and lining must be swimsuit material, so if you are unsure, ask for help where you are shopping to make sure they are both swimsuit fabric and swimsuit lining

Step 1: Print and prepare the pattern.

PDF patterns are great because you can use them over and over again, but the printing must be sized correctly, or else the entire project will be scaled too big or too small. The first page of the pattern has a test square on it. Print this page using a PDF reading software like Adobe Acrobat, making sure to print at 100% and not “scaled to the page” so it prints at the correct size. Measure the test page to make sure it’s correct. Once it is, print the remaining pages.

Need help with PDFs? Check out this post on how to print, assemble and trace PDF sewing patterns.

Step 2: Trim the pages.

Each PDF page will have a mess of lines and marks on it, all locked in by an outer rectangle. Trim up to this rectangle so you can match the lines on the pages to form the full pattern.

Tip: I like to only trim the right and bottom edges, so I can overlap the left and top edges with the pages next to it. I find this is easier than trying to line up two trimmed edges. You can use your paper scissors for this step or a rotary cutter as I have here.

Step 3: Assemble the pattern.

Each page has a point to match up to the page on either side of it. Match up the corresponding pages and lay them out into a large sheet. I use my floor for this step and make sure I have all my pages before taping anything together. Once you have them all in place, tape them all together to form the pattern.

Step 4: Cut the pattern.

Take a tape measure and measure your bust, hip, and waist and check them against the body measurements on the pattern. Remember, this is a bathing suit with negative ease, so that means that the finished size will be smaller than your body’s measurements, so make sure to look at the body size not the garment size on the chart, or else you will have a suit far too big for you. Once you’ve picked a size, cut out all of the pieces for the view you are making.

I don’t tape the entirety of every edge of every page, rather I place the tape at intervals along the way. After the pieces are cut, check to see that all the edges are taped down properly and tape along the back at any key spots as well.

Step 5: Cut the fabric.

When working with swimsuit fabric, it’s key to take your time. It is incredibly stretchy and slippery, so go slow and pin the pattern down a lot to keep it in place. Only use ball point pins to make sure the pins don’t puncture a hole through the fabric.

Keep in mind that while most patterns have a grainline on the pattern that is to be parallel with the selvage and lengthwise grain, this pattern has a line indicating the “greatest amount of stretch”. Be sure to place that line parallel to the crosswise or lengthwise grain, which ever stretches the most.

Cut the fabric once you have all the pieces pinned in place. If you are an experienced sewer, you could choose to use pattern weights and a rotary cutter for this step. Make your notch markings on your fabric, but do so with a water soluble marking tool instead of scissors as the project only has a 1/4″ seam allowance.

Step 6: Sew gather baste stitches.

Now it’s time to get to the sewing! But before we do, we need to talk a moment about machines. This fabric is stretch fabric and while many machines have “stretch” stitches, here we are not using those. You want to use a regular sewing machine straight stitch or zigzag stitch for many of these steps, and for some, a serger (overlock) machine is best. I will say which you should use at each step, so just read along and you’ll be fine. Also, make sure to change to polyester thread and 90/14 stretch needles for any machine to be used for the project. Before doing any sewing, be sure to test your stitches on your machine to make sure the feed and settings are working well with the fabric.

The first step to sew are two rows of baste stitches along each of the long sides of the two back pieces. The suit has a 1/4″ seam allowance unless otherwise noted, so make sure that both rows of baste stitches are within the 1/4″ seam allowance. Repeat by sewing two rows of baste stitches along the sides of the suit front piece.

Step 7: Gather the back.

Lay one back piece on top of a back lining. The lining piece is the size the back will be once the suit is gathered. Pull the baste stitches to gather the two back pieces until they match the size of the two back lining pieces. Pin in place at the top and bottom, even out the gathers, then pin along the gathered sides with the wrong side of the suit fabric facing the wrong side of the lining fabric.

Step 8: Sew back to lining.

For this step, use a regular machine with a long and narrow zigzag stitch. For reference, I used a width of 2.0 and a length of 3.0 for my stitch. Sew along the two long sides of each back piece that was pinned in place in step 8. Use a 1/8″ seam allowance for this stitch.

Step 9: Sew the legs.

At the bottom of each back piece, pin together the longest edge, which is part of the leg opening. The smaller part to the right of it in this photo is part of the crotch opening. If you have a serger machine, serge the leg seam. If not, use a regular sewing machine with a long and narrow zigzag stitch like used in step 9.

Step 10: Sew the center back.

Place the two back pieces on top of each other, right sides facing. Line up all the edges and pin them together along the center back, which is the shorter of the two sides.

Before you sew the center back seam, test your stitches. This seam has two layers of swimsuit fabric and two layers of swimsuit lining, so it is rather thick. If using a regular machine, run the same layers through the machine using a long and narrow zigzag stitch. If using a serger, which I highly recommend for the key construction seams like this one since they need to stretch and will be much more sturdy, test the tension and looper threads with the four layers.

Once you are confident in your stitch, sew the center back seam on the machine of your choice. Again, remember that this is sewn with a 1/4″ seam allowance.

Here is the back all assembled and ready to go! To the right is what goes around your bum, the V-shape to the left is the top of the center back, and the top and bottom sides in the image are the side seams.

Step 11: Assemble the front lining.

Lay the lower front piece on the front lining piece, wrong sides together. Pin along the curved front leg edges.

Sew along these two edges using a 1/4″ seam allowance on a serger machine if you have one. If not, use a long and narrow zigzag stitch on a regular machine.

Step 12: Sew the bust darts.

I trimmed my bust darts into the fabric so the extra flap of fabric was cut away. This is almost never done on regular garments, but with the swimsuit I wanted to reduce the bulk that the flap will create. You can choose to do either. Fold the fabric to line up the dart legs (or if you cut the fabric, line up the raw edges) and pin the dart in place.

I chose to sew the bust dart with my serger so it will stretch around my bust, but you can use a regular machine for this step if you like. Use a long and narrow zigzag stitch so it will stretch.

Step 13: Sew the lining to the bottom front.

Using a regular machine with a zigzag stitch, sew around the rest of the lower front along the top of the fabric, the side seams, and the crotch to tack the fabric to the lining. Stay within your 1/4″ seam allowance.

Step 14: Sew the crotch seam.

Place the front lining on top of the back piece, right sides facing. Pin along the crotch seam with the back fabric, the back lining, the front lining, and the lower front fabric all trapped in the seam.

Stitch the crotch seam in place. If you have a serger, use it for this step. If not, use a zigzag stitch on a regular machine.

Step 15: The bust line.

Use your pattern piece for the front of the suit and draw a line from the center of the sweetheart bust to the mark on the pattern that says “gather”. Be sure to use a water soluble marking tool that you have tested out on a scrap of the exact same fabric. Synthetics can behave unpredictably so it is always good to test first before marking on the center front of your project.

Using a regular sewing machine set to a long baste stitch, stitch down the left side of the line, 1/8″ away. At the bottom, pivot and sew to 1/8″ on the right side of the line. Continue sewing up the right side, 1/8″ away from the line so it is a continuous stitch from top to bottom and back up to the top again. Leave long thread tails to be pulled and knotted later.

Step 16: Sew the front tab.

Match up the notch marks on the tab piece and fold right sides together. Pin along the notched edge and sew it with the 1/4″ seam allowance. Use a serger if you have one for this step.

Just below the bottom of the line you drew in step 16, pin the tab in place with the right side down and the seam in the tab along the center of the side facing up. Stitch the tab in place along the short edge closest to the drawn line. I sewed this with a regular straight stitch on my regular machine, sewing back and forth a few times to secure it in place.

Step 17: Gather the front.

In step one, we sewed baste stitches along the sides of the front. Now it is time to gather those sides. Pull on the baste stitches to gather the front side seams to match the side seams of the back piece. This is where they will be sewn together, so they need to be the same size. Once they are the same length, even out the gathers and lock the stitches in place by winding the baste threads around a pin in a figure-eight so they cannot move. Set the front piece aside for the moment.

Step 18: Leg elastic.

Measure around the opening for the legs from the side seam of the back lining, around the crotch, to the side seam on the back. Cut a piece of elastic to this length. Make sure to use rubber elastic, so it performs correctly in the elements.

Pin the elastic in place on the wrong side of the fabric at the side seam on the front lining along the crotch. Only pin a couple of inches, lining up the elastic with the raw edge of the fabric. Mark a spot 3" from the side seam where the elastic is pinned. This is your stopping point. We are only going to sew that little bit.

Before you sew, test the stitch on a scrap of two layers of fabric and a layer of elastic since this is the first time we are sewing through the elastic. For this step you want to use a wider zigzag stitch. For reference, I used a 4.0 width and 3.0 length for this stitch in the image above. Once you are happy with the stitch, sew the elastic to the edge from the side seam to the 3" stopping point.

Roll the elastic to the wrong side of the suit so the elastic is sandwiched in the lining. Change to a medium zigzag stitch and sew from the side seam to 1.5" onto the elastic. Mark the stopping point before starting — make sure to keep your stitch near the edge of the fabric to the inside of the suit. I used a 2.0 width and a 2.5 length for my stitch. Repeat on the other leg opening side seam. Set this aside for the moment.

Step 19: Optional bra cups.

The suit has no support in the bust other than the fabric itself, so I knew I wanted to include bra cups in mine as all my favorite suits have this kind of support. I've seen many other bloggers use these and it seems like they worked quite well. Make sure to purchase bra cups meant for swimsuits or else they will possibly absorb the water in a weird way, making your bust area soaked with water. Not good!

I wanted to insert my cups into its own shelf bra to include like its own layer on the inside of the suit. If you'd prefer to insert them into the suit lining on its own, you can do that too. But, this is a good time to consider this option since we are about to assemble all the elements together.

For my shelf bra, I cut 7" from the top of the sweetheart bust down the front lining piece then across to the side seams. Sew the bust darts the same way you did on the lining so they match. Place one of the cups on the lining piece. To aid with this, I used a pressing ham under the cup so it could lay in correct position during the pinning. Pin around the cup and repeat on the other side. Before sewing them on, try the lining onto your body to ensure the cup placement is correct.

Note: Remember that the lining side of the shelf bra will be up against your body, not the cups themselves.

Using a medium zigzag stitch, sew around the cups, securing them to the shelf bra.

Cut a piece of elastic that will go along the bottom of the shelf bra. I held the elastic up to my body where my bra ends and stretched it very slightly around my chest then cut it there. You don't want this to be tight, but if it is loose it will create wrinkles under the lining of your suit which might be uncomfortable and visible.

Sew the elastic to the wrong side (the side with the cups) of the shelf bra along the lower edge. Use the same wide zigzag stitch you used in step 19 to sew the elastic to the leg opening. The elastic doesn't need to be folded and top stitched as the elastic will not be facing the body but rather will be facing the lining.

Pin the shelf bra to the front lining along the top and sides with the wrong side of the shelf bra facing the wrong side of the lining (the side without the lower front sewn to it). Stitch the bra in place along the pinned edges with a long and narrow zigzag stitch inside the 1/4" seam allowance. This will now just be part of the lining from this point forward.

Step 20: The side seams.

Place the back down flat, right side up. Lay the front piece down on top of it, right side down. Line up the side seams and pin together along the gathered edges.

Next, fold the front lining (that is attached to the back at the crotch) on top of the wrong side of the front. Match the notches along the side seams so the top of the suit lines up at the side seams and ends higher than the lower part of the front (that part is the skirt-like area at the lower front and is longer than the suit front which will be under the skirt). Pin the lining in place along the side seams through all the layers.

Sew along the side seams through the lining, front, and back. Before doing this, I would suggest testing that many layers on your machine to make sure the settings are correct for that thickness. Also, use a serger for this step if possible. Otherwise use a zigzag stitch on a regular machine.

Step 21: The leg openings.

In step 19 we attached the elastic at the leg so it could be sewn into the side seam in the last step. Now we need to continue the stitching for the rest of the leg opening. As pointed out in the pattern's instructions, the elastic shouldn't be distributed equally around the leg opening since we need it gathered in some spots but not others. These steps might seem odd, but follow along and it will work!

Measure the distance around the leg opening from where the elastic is already sewn to the other side seam. Mark a spot 2/3rds of the way along that measurement. Sew to that point with the same wide zigzag used previously and stop.

Measure the remaining distance from where you just stopped to the side seam. Calculate 70% of that measurement by multiplying the number by .7. This is your new length. Cut the remaining elastic to this measurement.

Divide the unsewn elastic into fourths and mark with a water soluble pen. Do the same with the leg opening left to be sewn.

Pin the elastic to the leg opening, at the four market spots.

Using the same wide zigzag stitch, sew the elastic to the leg opening, stretching the elastic to fit the distance as it is now 30% shorter after cutting, which will gather the suit to our bum. Repeat on the other side so both legs are sewn with elastic.

Step 22: Lower front.

We now need to add elastic to the lower front edge of the suit. This will be cut the same length as the fabric, so simply lay the elastic (or a tape measure) along the lower front edge and cut to match. Pin in place close to the raw edge of the fabric, overlapping the ends of the elastic with the ends of the elastic on the leg openings. Sew in place with the same wide zigzag stitch used in the last step.

Step 23: Finish the lower edge.

The lower front and the leg openings are now all sewn with elastic and one long continuos seam. The elastic now needs to be folded to the inside as we did in step 19. Fold the elastic to the wrong side so it is sandwiched in the lining and pin in place all along the lower opening and leg holes.

Sew the fold in place with a medium zigzag stitch, sewing close to the inside edge. When sewing around the area that is gathered with elastic, pull the elastic to prevent puckers from being stitched into the seam.

Step 24: Front gathering.

Pull on the baste threads at the center front until the area is gathered as much as possible. Tie the threads into a knot to hold them in place.

Step 25: Upper elastic.

Pin around the upper opening, pinning the front to the front lining and the back to the back lining. Sew the layers together by stitching around the upper edge. Use a serger for this stitch if possible. Otherwise use a zigzag stitch.

Measure around the upper opening and cut your elastic to match that distance. This is a good moment to try on the suit to see if there is any gaping along the top edge. If so, you can cut the elastic slightly shorter so the top edge is gathered in slightly.

As with the other steps, stitch the elastic to the edge of the fabric with a wide zigzag stitch, overlapping the ends slightly. Fold the elastic to the inside, pin in place, then sew with a medium zigzag stitch all around the top opening edge.

Step 26: The tab.

Fold the tab at the center front to the inside of the suit. The bottom of the tab on the inside should pass the end of the tab on the right side. Pin and baste the tab in place using a regular machine baste stitch.

On the right side of the suit, use a regular straight stitch and stitch the tab in place by stitching in the ditch just under where the tab was sewn. Make sure to catch the inside of the tab at the same time. Remove the baste stitch and trim the tab if necessary on the inside of the suit.

Step 27: The straps.

First off, take a sigh of relief, as this is the last step! Well done! Okay, all we have to do is fold the straps along the long edge, right sides facing. Pin along the long side as well as the shorter (more narrow) of the two ends. Stitch the short end and the long side with a serger if possible, or a zigzag stitch, using the 1/4" seam allowance.

Carefully turn the straps right side out. Poke out the ends using something pointy but not sharp. Sew the open end of each strap with a serger or zigzag stitch.

Pin the straps to the suit on the inside of the top with the notches matching. Sew in place with a medium zigzag stitch in line with the stitching already present from sewing the elastic.

Well done! That's it! Try your new suit on and tell me if you don't feel like a bombshell goddess?! Everyone online raved about how flattering this suit is, and for me, I can hands down agree with this. I hope you feel the same and that this tutorial was helpful!

August 17, 2014
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How to Sew a Swimsuit You'll Really Love