What You Need Before You Start

Sewing a bathing suit is different from sewing everyday clothes because swimwear fabric stretches, needs to move with your body, and has to withstand chlorine or saltwater. You will need swimwear fabric (usually a nylon-spandex blend called swimsuit knit or lycra), elastic for the leg openings and waistband, a serger or a sewing machine with a ballpoint needle, and thread designed for stretch fabrics. A regular sewing machine works if you use a ballpoint needle and a stretch stitch, but a serger finishes the seams more neatly and is less likely to snap threads under tension.

You will also need a pattern. Simplicity, McCall's, and Butterick all make swimsuit patterns in a range of sizes, and you can find them at fabric stores or online. Patterns come with instructions specific to swimwear construction, which is important—the order of steps is different from a regular garment because you attach elastic as you go rather than after. Read the pattern instructions all the way through before you cut anything.

Swimwear fabric is slippery and stretches in all directions, so lay it out on a flat surface, pin the pattern pieces down firmly, and cut slowly. Mark the grain line on your pattern pieces with a pen so you know which direction the stretch runs—this matters for fit.

Key Takeaways

  • Swimwear requires a ballpoint needle, stretch thread, and a serger or stretch stitch on your regular machine because regular needles and stitches will snap under the fabric's movement.
  • Elastic goes in as you sew the seams together, not after, so follow your pattern's order of assembly exactly or the suit will not fit.
  • Swimwear fabric stretches in all directions and is slippery, so pin your pattern down firmly and cut slowly to avoid shifting.
  • A test garment in muslin or cheap knit fabric saves time and frustration because fit is harder to judge on stretch fabric than on woven cloth.
  • Seams must be finished or sealed because raw edges will fray in water and the suit will fall apart within a few wears.

Preparing Your Pattern and Fabric

Before you cut, decide whether to make a test garment. Swimsuit fit is tricky because the stretch changes how the suit sits on your body, and a mistake in the pattern size is hard to fix once you have sewn the seams. Many sewers make a test version in cheap knit fabric or muslin first, wear it, and adjust the pattern before cutting the real fabric. This takes an extra day or two but saves money and frustration.

Lay your swimwear fabric on a flat surface with the pattern pieces pinned down. Swimwear fabric curls at the edges and moves easily, so use plenty of pins and weight it down with books or pattern weights if you have them. Cut slowly and follow the grain line marked on your pattern. Do not stretch the fabric as you cut—let the scissors do the work.

Mark all the notches, darts, and seam lines on your fabric pieces with a fabric pen or tailor's chalk. These marks tell you where seams meet and where elastic goes, so accuracy here saves time later.

Sewing the Main Seams

Thread your machine with stretch thread (polyester or nylon thread made for swimwear) and insert a ballpoint needle, size 75/11 or 80/12. A ballpoint needle slides between the fibers of stretch fabric instead of piercing them, which prevents laddering (runs) and broken threads. If you have a serger, use it for all seams—it finishes and seals the edges in one pass, which is ideal for swimwear.

Start with the shoulder seams. Place two pieces right sides together, pin, and sew using a stretch stitch (on a regular machine) or a 3-thread serger stitch. Sew slowly and do not pull the fabric—let the machine feed it. Stretch stitches look like a zigzag and flex with the fabric instead of snapping when you move.

After you sew each seam, trim the seam allowance to 1/4 inch and finish the raw edges. If you have a serger, it does this automatically. If you are using a regular machine, use a zigzag stitch along the raw edge or a 3-step zigzag if your machine has one. This stops the fabric from fraying in water.

Attaching Elastic to Leg Openings and Waistband

Elastic goes in before you close the side seams, so follow your pattern's order. Cut elastic to the length specified in your pattern—usually 1 to 2 inches shorter than the opening it will cover, because the elastic pulls the fabric in. Pin the elastic to the wrong side of the fabric, stretching it slightly as you pin so it lies flat.

Sew the elastic down using a stretch stitch or serger, sewing slowly and letting the elastic guide the fabric. The elastic will bunch slightly as you sew, which is normal. Once you have sewn it, the fabric will pull up and the bunching will disappear. Fold the elastic to the inside and sew it down again from the right side using a narrow zigzag or a cover stitch if your machine has one. This second row of stitching keeps the elastic from rolling and makes the finish look professional.

Repeat this for all leg openings and the waistband. The waistband elastic is usually wider (1 to 1.5 inches) and goes in the same way.

Closing the Side Seams and Final Finishing

Once the elastic is attached to the legs and waist, close the side seams. Pin the front and back pieces right sides together, matching the elastic seams, and sew using your stretch stitch or serger. Trim and finish the seam allowance as before.

Try the suit on inside out to check the fit. Swimwear should be snug but not painful—you should be able to fit one finger under the waistband and leg elastic. If it is too loose, you can take in the side seams slightly, but if it is too tight, you will need to let out the seams or start over. This is why a test garment is worth the time.

Once the fit is right, turn the suit right side out and try it on again. Check that the elastic lies flat, the seams are straight, and there are no puckers or loose threads. Trim any loose threads and seal any raw edges you missed.

Sealing Seams for Water Resistance

Swimwear seams need to be sealed so water does not seep through and the fabric does not fray. If you used a serger, the seams are already sealed. If you used a regular machine, explore a seam sealer—a flexible fabric glue made for swimwear—along the inside seams. explore it with a small brush or the applicator bottle, following the product instructions. Let it dry completely (usually 24 hours) before wearing the suit.

Alternatively, you can use a cover stitch or a narrow zigzag along the seam allowance to seal it. Some sewers use both methods for extra durability, especially on the waistband and leg openings where stress is highest.

Caring for Your Finished Suit

Rinse your new suit in fresh water after every wear, especially if you swam in chlorine or saltwater. Wring it gently—do not twist or wring hard, which stretches the fabric. Lay it flat to dry or hang it in the shade. Do not put it in the dryer or leave it in direct sunlight for long periods, as heat and UV light break down the spandex and cause fading.

Wash the suit by hand in cool water with mild soap every few wears, or after heavy chlorine exposure. Machine washing and hot water shorten the suit's life. A well-made swimsuit should last one to two seasons with proper care.

Frequently Asked Questions

Can I use a regular sewing machine to sew a bathing suit?

Yes, but you must use a ballpoint needle and a stretch stitch. A regular needle will break threads and create runs in the fabric. A stretch stitch (usually marked with a zigzag symbol on your machine) flexes with the fabric instead of snapping. A serger is better because it finishes seams in one pass, but a regular machine works if you finish the seam allowances by hand afterward.

What is the difference between swimwear fabric and regular knit fabric?

Swimwear fabric is a nylon-spandex blend designed to withstand chlorine, saltwater, and repeated stretching. Regular knit fabric (like t-shirt knit) breaks down quickly in water and loses its shape. Swimwear fabric is more expensive but lasts much longer and holds its fit better. You cannot substitute regular knit for swimwear fabric.

Why does my bathing suit pucker at the seams?

Puckering usually means you pulled the fabric as you sewed or used the wrong needle or stitch. Let the machine feed the fabric—do not guide it. Use a ballpoint needle and a stretch stitch, and sew slowly. If puckering happens after you have already sewn, you may need to pick out the seam and resew it.

How do I know what size pattern to buy?

Swimwear patterns run differently than clothing patterns, so measure your bust, waist, and hip and compare them to the pattern envelope's size chart. Most patterns include a finished garment measurement chart on the back, which tells you how much ease (extra room) is built in. For swimwear, you want minimal ease—usually 0 to 1 inch—so the suit fits snugly without being restrictive.

Can I add padding or cups to my homemade bathing suit?

Yes, but you need to sew them in before you close the side seams. Swimwear padding and cups are made from the same stretch materials as the suit fabric and come with instructions for placement. Pin them to the wrong side of the front pieces, sew around the edges using a stretch stitch, and trim the seam allowance. Then proceed with sewing the seams as normal.