What You Need Before You Start
Sewing a swimming suit is different from sewing regular clothes because the fabric moves with your body and has to withstand chlorine, salt water, and constant stretching. You will need swimsuit fabric — usually a nylon-spandex blend called lycra or swimwear knit — not cotton or regular jersey. Cotton absorbs water and loses shape; swimsuit fabric sheds water and snaps back.
Beyond fabric, gather a ballpoint or stretch needle (size 75/11 or 80/12), thread made for stretch fabrics, a serger or a sewing machine with a stretch stitch, elastic for the leg openings and waistband, and a pattern. Most swimmers use commercial patterns from companies like Simplicity, McCall's, or Vogue — these come with the correct seam allowances and shaping already built in. You can also find free patterns online through sites like Etsy or sewing blogs, but check the reviews first to see if the fit matches your body type.
Key Takeaways
- Swimsuit fabric is a nylon-spandex blend that must be cut and sewn differently than regular cloth because it stretches in all directions.
- A ballpoint needle and stretch thread are required; regular needles will skip stitches and regular thread will snap when the suit moves.
- A serger produces the most durable seams because it locks the raw edges, but a sewing machine with a stretch stitch or narrow zigzag works if you finish the seams afterward.
- Patterns designed for swimwear already account for the stretch and recovery of the fabric, so using a regular dress pattern will result in a suit that is too tight or too loose.
- Elastic at the waist and leg openings must be applied with a stretch stitch to prevent the elastic from snapping when you move.
Preparing Your Pattern and Fabric
Lay out your pattern pieces on the swimsuit fabric with the stretch running vertically (up and down your body). Most swimwear patterns are designed so the greatest stretch goes across your chest and hips, not lengthwise. Pin the pattern pieces down lightly — do not use heavy pins that will leave holes — and cut slowly with sharp scissors or a rotary cutter. Swimsuit fabric is slippery and will shift if you rush.
Before you cut, check the pattern instructions for grain line direction. Some patterns ask you to cut the front and back on the fold; others ask you to cut two separate pieces. Follow the pattern exactly. If you cut the wrong way, the suit will pull to one side or feel uncomfortable in the water.
After cutting, mark the notches and construction lines with a fabric pen or tailor's chalk. Do not use a regular pen — it will bleed into the fabric. Lay all your pieces flat on a clean surface and double-check that you have cut everything before you start sewing.
Sewing the Main Seams
Start by sewing the shoulder seams. Set your machine to a stretch stitch (often labeled as a lightning bolt or a wavy line on the dial) or use a narrow zigzag stitch set to 2.0 width and 2.5 length. A straight stitch will snap when you put the suit on. Place the two shoulder pieces right sides together, pin, and sew slowly. Swimsuit fabric does not need pinning every inch — pin at the notches and every 3 to 4 inches — because too many pins create holes.
After sewing the shoulders, sew the side seams. This is where the suit takes shape. Pin the front and back pieces together at the side, matching the notches, and sew with the same stretch stitch. Press the seams flat with a cool iron — high heat will melt the spandex. If you have a serger, run the seams through it now to lock the raw edges and prevent fraying. If you do not have a serger, trim the seam allowance to 1/4 inch and finish the edges with a narrow zigzag stitch.
Sew the inseams (the seams that run between your legs) next. This seam takes the most stress, so make sure your stitch is set to stretch mode. Sew slowly and do not pull the fabric — let the machine feed it through on its own. Pulling will stretch the seam out of shape and create a baggy crotch.
Attaching Elastic to the Waist and Legs
Cut elastic for the waist and leg openings. The elastic should be 1 to 2 inches shorter than the opening it will cover — this creates the tension that holds the suit in place. For example, if your waist opening measures 28 inches, cut the elastic 26 to 27 inches long. Overlap the ends of the elastic by 1/2 inch and sew them together with a zigzag stitch to form a loop.
Pin the elastic to the inside of the waist opening, dividing both the elastic and the opening into four equal parts and matching the pins. The elastic should be on the inside of the suit, against your skin. Sew the elastic down using a stretch stitch, stretching the elastic as you sew so it lies flat against the fabric. Do not stretch the fabric itself — only the elastic. This is the hardest part of the project because you have to hold tension on the elastic while the machine is moving, but it is what keeps the suit from rolling down in the water.
Repeat this process for the leg openings. Measure each opening, cut elastic 1 to 2 inches shorter, overlap and sew the ends, pin it to the inside of the leg opening, and sew it down while stretching the elastic. The leg openings should feel snug but not painful when you try the suit on.
Finishing the Neckline
The neckline can be finished three ways: with elastic binding, with a fold-over elastic, or with a straightforward rolled hem. Fold-over elastic is the easiest for beginners. Cut a length of fold-over elastic that is 1 to 2 inches shorter than your neckline opening, overlap the ends by 1/2 inch, and sew them together.
Open the fold-over elastic and pin it to the neckline opening, matching the center front and center back. The elastic should wrap around the raw edge of the neckline. Sew it down using a stretch stitch, stretching the elastic as you sew. When you are done, fold the elastic to the inside of the suit and topstitch it down with another stretch stitch to find it permanently.
If you prefer a binding, you can cut 1.5-inch strips of swimsuit fabric, sew them into a loop, and attach them the same way. Binding takes longer but looks more professional and is easier to adjust if the neckline is too tight or too loose.
Trying On and Adjusting the Fit
Put the suit on and check the fit in a mirror. The suit should feel snug but not restrictive. If the leg openings are too loose, you can remove the elastic and cut it shorter, then re-sew it. If the waist is too tight, you can remove the elastic and replace it with a longer piece. These adjustments are easier to make now than after you have worn the suit in the water.
Check that the suit does not gap at the armholes or neckline. If it does, the elastic may need to be tighter. Check that the crotch seam sits in the right place — it should not pull to one side or ride up. If it does, the side seams may need to be adjusted, which means you will have to take the suit apart and re-sew them. This is why using a pattern designed for your body type matters: it reduces the chance of major fit problems.
Once the fit is correct, try the suit on one more time after washing it in cool water. Swimsuit fabric shrinks slightly when wet, so the suit may feel tighter after the first wash. If it is too tight, you may need to adjust the elastic again.
Caring for Your Finished Suit
Rinse your new suit in cool fresh water when ready after wearing it in chlorine or salt water. Chlorine and salt break down the spandex and cause the suit to lose elasticity. Wash it by hand in cool water with a gentle detergent — do not use the washing machine, which agitates the fabric and causes pilling. Lay it flat to dry, never in direct sunlight, because UV light also breaks down spandex.
A well-made swimsuit will last one to two seasons of regular swimming if you rinse and dry it properly. If you notice the elastic losing tension or the fabric becoming thin, it is time to make a new one. The skills you learned on your first suit will make the second one faster and easier.
Frequently Asked Questions
Can I use a regular sewing machine or do I need a serger?
A regular sewing machine works if it has a stretch stitch or zigzag option. A serger produces neater seams and locks the raw edges so they do not fray, but it is not required. If you do not have a serger, finish the seams with a narrow zigzag stitch after sewing them with a stretch stitch.
What if my pattern does not come with elastic measurements?
Measure the waist and leg openings of the pattern pieces and cut elastic 1 to 2 inches shorter than each measurement. The exact amount depends on how snug you want the suit to feel — less elastic means a tighter fit. Test on a scrap piece of fabric first if you are unsure.
Why does my suit feel loose in the water even though it fit snugly on land?
Swimsuit fabric stretches more when wet. If the suit is too loose after swimming, the elastic may be too long or the fabric may have lost some of its recovery. Rinse and dry it completely, then try it on again. If it is still loose, you can remove the elastic and replace it with a shorter piece.
Can I use regular thread or do I need special stretch thread?
Regular thread will snap when the suit stretches. Use thread made for stretch fabrics or polyester thread, which has some give. Avoid cotton thread entirely — it will break the first time you move in the water.
How do I know if my pattern size is correct?
Most swimwear patterns are sized by bust measurement. Measure around the fullest part of your chest and compare it to the pattern envelope. If you are between sizes, choose the smaller size — swimsuit fabric stretches to fit, and a suit that is too big will not hold you properly in the water.