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How to Alter a Bathing Suit

I really didn’t appreciate the destructive environmental and humanitarian impacts of fast fashion until I was well on my way to a foundational understanding of fashion design and construction. I was initially motivated to learn to sew by a desire to have clothes that fit my body and my lifestyle. I was tired of shorts that were too loose in the waist and too tight at the thighs, pants that were too low, and dresses that didn’t hide bra straps. Perhaps more than anything, I was tired of the rush of insecurity that arose when the dressing room mirror reflected my body in an ill-fitting garment. The worst offender of body misrepresentation in my opinion? Bathing suits. 

I’ve come a long way over the past 15 years in my journey of learning to love my body, but the feelings of inadequacy and freakishness that plagued my middle and high school years seemed to rush back when I put on a sore-bought bathing suit. The body that I’ve become so fond of suddenly seemed uncomfortable, pinched, flabby, and just-not-right. 

I think fast fashion has come a long way in the diversity of suits offered over the past 5+ years. Why it took this long for high-waisted bikini bottoms to come back into vogue is beyond me, but they are certainly here now! More “cheeky” styles have also become prevalent, which may not be for everyone but is certainly my preference. I am glad to see more offerings between the itsy bitsy string bikini and grandmas-only skirted one pieces, but now that I’ve gotten the taste for suits custom fit to my body, I’ll never go back.

Before RTW stiped bathing suit
Altered striped bikini

The Thinking

I’ve created a few suits from scratch, but here I’d like to talk about the store-bought suit I recently altered for an improved fit. The original piece was actually a maternity suit I bought at Target maybe 5 years ago. This speaks not to my intention to become pregnant, but my desperation to find a bathing suit that didn’t make me want to skip the beach. I really liked the colors of the stripes and was glad it offered a little belly modesty, but I never enjoyed wearing it for a few reasons:

  • I purchased a small so the belly wouldn’t have way too much extra fabric, but I am not a small. I typically wear a Large or an XL if the garment stretches across my hips or up my torso so this small was a bit tight vertically. 
  • The extra fabric at the belly gave off some serious frumpy vibes. 
  • The bum was cut really wide and the hips were cut too low. 
  • One pieces are tempting because they cover the belly but I find them less convenient (for bathroom use) and less comfortable than two piece alternatives. 

The Process

Given these issues, I was thinking I would need to convert this one piece to a two piece but decided to first start by raising the hip and thinning the bum to see if that gave me enough vertical ease. After doing that, the vertical fit was still too tight, so I chopped it into two. 

Determining the new leg cut

  • Put on the suit and use chalk (or any marking tool that comes off in the wash) to sketch out the approximate leg hole you want. If you have another suit or a pair of underwear that has a flattering cut, put those on top of the piece you’re altering and use that to guide your marks. 
  • Take off the suit and use a french curve (or a careful eye) to turn your markings into a clean line. Put the suit back on and fold it under along the new line as best you can to make sure you like how it looks. 
RTW striped bathing suit folded in half with weights
  • Use your trusty stitch ripper to rip up the hem stitches of any portion of the leg hole that you don’t want to change or only want to reduce by ⅜” or less. Anything you want to reduce by more than ⅜” will be cut off anyway. It may seem counterintuitive to rip the stitches of portions you don’t want to change but this will allow you to create a clean finish throughout the leg hole.
  • Next, mark a new line ⅜” out from the line you’ve finalized. Cut along this new line. 
  • Fold the suit along center front and center back, matching side and crotch seams. Cut the second side so the right and left sides are symmetrical.

Finishing the leg hemlines

A lot of what I’ve read about sewing swimwear online has suggested using a zig zag stitch on a regular sewing machine to attach the elastic and to finish the hem. But I have had the most luck achieving a professional finish by using a serger with the trimmer disengaged to attach the elastic and a twin needle on my regular sewing machine to finish the hem. If you don’t have a serger, I actually recommend this blog post (not endorsing here – it’s a subsidiary of Amazon and I definitely prefer to source my materials at thrift shops and small businesses where ethics, sustainability, and quality are prioritized). If you’re intimidated by twin needles, I recommend you face your fear and give it a whirl! They really don’t require a special skill set but offer a RTW looking finish. For general reference on sewing swimwear (or anything sewing, really) I highly recommend the Love to Sew podcast.

Leg hem of RTW striped bathing suit
Finished Hem of striped bathing suit
  • Starting with the front piece of the suit, pin about 4” of ⅜” swim elastic to the wrong side of the fabric with the raw edge of the fabric lined up with the edge of the elastic. 
  • Using a serger (with the trimmer disengaged), start sewing the elastic to the leg hole. I find it easier to work with the elastic facing down and the fabric facing up because the elastic tends to get stuck on my presser foot but it makes it a little more difficult to keep the raw edge and the elastic lined up so experiment with a scrap piece to see what works best for you. Don’t stretch the elastic or the fabric until you get to the crotch seam. 
  • At the crotch seam, start pulling the elastic as you go. Since the bottom of your butt is likely where the most dramatic curve is, start reducing how much you pull the elastic as you get past the first third of the back piece. My butt is pretty flat and this worked well for me but I would imagine the rounder your butt is, the longer you’ll want to pull the elastic as you make your way to the side seam. 
  • Stop a few inches before you meet where you started, lay the elastic along the raw edge and trim it so that there is room to overlap the starting piece by about ¼”. Continue sewing about ½” past where you started.
  • Fold the edge over the elastic and secure at least a few inches with pins or clips (I prefer clips for this sort of thing). 
  • Using a twin needle with right side facing up, sew the folded over edge so that one needle catches the elastic and the other is just past the raw edge (which is folded under and not visible so this can be tricky to line up – if you’re struggling, veer towards the edge of the garment as it’s most important to catch the elastic). This will ensure a beautiful twin stitch on the right side of the garment and a smooth and secure finish on the wrong side of the garment.
  • Repeat for the other leg hole.

Finishing the waist hem

I knew I wanted the bottoms to be high waisted because I want almost everything to be high waisted. Since I would still have plenty of fabric at the top to work with, I decided to make them as high as I could given the dip in the back and planned to adjust if needed, but this ended up being a perfect height.

  • Cut a straight line ⅜” above wherever you want the piece to hit your torso. 
  • Try on the piece and wrap a ⅜” swim elastic around your waist at the point the piece hits your torso. Play around with the length of the elastic until it feels like it is just slightly stretched but not so tight that it is uncomfortable. The more curvy your hips are, the looser you can make the elastic without the piece falling off. Trim the elastic where it meets itself after circling your body. 
  • Attach the two ends of the elastic by using a wide zig-zag stitch. 
  • Fold the elastic loop at this connection and mark the exact opposite side. Then hold the connection and this mark together to find and mark half way between in both directions so the loop is divided in 4 equal parts by the markings plus the connection.
  • Similarly, lay the garment flat and mark either end of the waist. Then connect those two marks to find and mark half way between in both directions so the garment waist is also divided in 4 equal parts by the 4 markings. 
  • Pin the swim elastic to the wrong side of the waist with the raw edge of the fabric lined up with the edge of the elastic, matching each marking of the elastic with a marking on the garment.  Depending on the width of your waist and your skillset you may want to add additional pins so the elastic is evenly stretched across the entirety of the waist fabric.
  • Sew the elastic in place using a serger (with the trimmer disengaged), similar to as was done for the leg holes. 
  • Repeat the steps described above to fold the edge over the elastic and secure using a twin needle.

Finishing the bikini top

I’m not going to go into the details of how I finished the top because the specific steps would only be applicable to similar designs. Essentially, I trimmed the fabric under the bust so there was 1” left then folded that over to create a casing for ⅜” elastic. Then I folded the top layer of fabric, which wrapped across the chest, to secure the raw edges and the ⅜” elastic I had inserted into the casing. 

Bikini top with additional fabric under bust

The Point?

If you’re struggling to find a bathing suit that works for your body, take a break from any efforts to change that body and instead try to change the garment you’re putting it in. For me, this was a powerful shift in thinking. In my me-made and altered suits the cellulite on my thighs and rolls on my back don’t disappear, but doubts I had about them seem to.

Before RTW stiped bathing suit
Before RTW stiped bathing suit
After altered striped RTW bathing suit (back view)
After altered striped RTW bathing suit (front view)