How to Sew a One-Piece Swimsuit from Stretch Fabric | DIY Sewing Tutorial
, by Vasil Shyshou, 12 min reading time
Sewing your own swimsuit is easier than you think — and the result fits your body perfectly. Here's everything you need to get started, from fabric choice to finished elastic edges.
How to Sew a One-Piece Swimsuit from Stretch Fabric — DIY Tutorial
Summer calls for a swimsuit that fits like it was made for you — because it was. Sewing your own one-piece swimsuit from stretch fabric is a satisfying beginner-to-intermediate project that gives you full control over fit, color, and style. In this step-by-step guide, we'll walk through the entire process from cutting to finished edges.
Difficulty: Beginner–Intermediate Time: Approx. 3 hours Cost: $15–$30 depending on fabric choice
What Fabric to Use for a DIY Swimsuit
The right fabric makes all the difference. For swimwear, you need a material that stretches in all four directions, holds its shape when wet, and doesn't go transparent when damp.
The best choice is a four-way stretch swimwear fabric — sometimes called biflex or spandex tricot — with a composition of around 80% nylon and 20% spandex (elastane). At KAHANNE Fabrics we carry jersey and rib knit fabrics that work beautifully for this type of project.
Key fabric requirements:
- Minimum weight: 200 GSM — lighter fabrics may become see-through when wet
- Four-way stretch in both directions
- Quick-dry and chlorine-resistant composition preferred for pool use
- Avoid light colors unless you're adding a lining layer — even dense fabrics can become translucent when wet
This same pattern can also be made as a bodysuit using single jersey or rib knit fabric. The key is choosing a material with strong recovery — it should spring back after stretching.
Materials You'll Need
- Stretch swimwear fabric (approx. 80 cm / 32 inches) — four-way stretch, minimum 200 GSM
- Stretch mesh fabric (approx. 20 cm / 8 inches) — for the cup pocket lining
- Polyester thread — use a thread designed for stretch fabrics; standard thread will snap under tension
- Stretch sewing needle — size 75/11 recommended (look for "super stretch" or "ballpoint" needles)
- Latex elastic 5mm wide — approx. 3 meters total
- Silicone grip tape 6mm — approx. 50 cm (used along the bottom of the cup area)
- Foam bra cups — optional, inserted through the strap opening at the end
- Cotton jersey fabric — a small piece for the inner gusset lining (optional but recommended for hygiene)
Equipment needed: sewing machine with zigzag stitch capability, serger/overlock machine (strongly recommended)
Step-by-Step: How to Sew a One-Piece Swimsuit
Step 1 — Cut Your Pattern Pieces
Using your chosen pattern (a classic one-piece pattern works well — free patterns are widely available online for various sizes), cut the following pieces:
- Front body panel — from stretch fabric
- Back body panel — from stretch fabric
- Gusset — from stretch fabric (cut two if using a cotton inner lining)
- Cup pocket — from stretch mesh fabric
Mark the center point of each piece before you start pinning — it makes alignment much easier and keeps everything symmetrical.
Step 2 — Cut the Cup Pocket
Fold the mesh fabric double and lay it over the front panel, slightly overlapping the shoulder straps. Pin it in place. From the armhole line, measure down 10–14 cm (4–5.5 inches) and trim the mesh along that line, cutting it exactly to the front panel edges.
Step 3 — Mark the Center Line of the Cup Pocket
Find the center point between the two armholes and mark a straight vertical line down the mesh piece. This dividing line prevents the cups from shifting sideways once inserted.
Step 4 — Stitch the Cup Pocket Divider and Attach Silicone Tape
Using a zigzag stitch (1mm wide, 2.5mm long), sew along the marked center line. Then lay the silicone grip tape along the bottom raw edge of the mesh and stitch it in place with a wider zigzag (3mm wide, 2.5mm long). Do not stretch the tape as you sew — keep it flat.
Step 5 — Pin the Cup Pocket to the Front Panel
Pin the finished mesh piece to the wrong side of the front body panel, aligning all edges carefully.
Step 6 — Join Side Seams
Place the front and back panels right sides together and pin along both side seams. Ease the fabric gently as you pin to avoid puckering — stretch fabric needs to be handled without tension when pinned.
Step 7 — Serge the Side Seams
Sew the side seams on your serger/overlock machine. If you don't have a serger, use a narrow zigzag stitch on your sewing machine — never use a straight stitch alone on stretch fabric.
Step 8 — Serge the Shoulder Seams
Pin the front and back panels right sides together at the shoulder straps and serge those seams as well.
Step 9 — Prepare the Gusset
If using a double gusset (recommended for swimwear), layer the cotton inner piece and the stretch fabric outer piece wrong sides together. The gusset should be approximately 1 cm narrower on each side than the main panels — this is intentional and helps everything lie flat.
Pin the cotton gusset piece to the wrong side of the back panel bottom edge, then pin the stretch fabric gusset on top. Sandwich the front panel over the top, right sides facing, and serge all layers together. You can hand-baste first to keep everything in place under the machine.
Step 10 — Finish the Gusset Opening
Zigzag stitch along the open raw edge to join the two gusset layers. Fold the gusset lining toward the inside of the front panel and pin, leaving approximately 1 cm exposed at each edge. Baste in place.
Step 11 — Calculate Leg Opening Elastic
Measure the total circumference of one leg opening. Multiply by 0.95 to get your elastic length. For example: 60 cm opening × 0.95 = 57 cm of elastic.
Step 12 — Attach Leg Opening Elastic
Distribute the elastic evenly around the leg opening on the wrong side of the fabric and pin. Serge in place using a 3-thread overlock stitch (remove the right needle to switch to 3-thread mode). Keep gentle tension on the elastic as you sew — watch that it doesn't slip under the serger foot. Tuck thread tails back into the seam using a hand needle with a wide eye.
Step 13 — Topstitch the Leg Elastic
Fold the elastic to the wrong side and topstitch over it using a wide zigzag stitch. Work with both hands — stretch the elastic in front with your right hand and behind with your left for even tension throughout.
Test your zigzag width and stitch length on a scrap piece first to find the right settings for your elastic width.
Step 14 — Calculate Armhole Elastic
Measure the armhole opening and multiply by 0.95. Example: 45 cm × 0.95 = 42.75 cm.
Step 15 — Attach Armhole Elastic
Attach and topstitch the armhole elastic using the same method as the leg openings. Make sure the mesh cup pocket is well-basted to the front panel before this step so it doesn't shift during sewing.
Step 16 — Calculate Neckline and Back Elastic
Measure the back edge and the neckline separately, as they use different coefficients:
- Back edge (higher tension needed): multiply by 0.85 Example: 86 cm × 0.85 = 73.1 cm
- Neckline: multiply by 0.90 Example: 51 cm × 0.90 = 45.9 cm
The back uses a smaller coefficient so the fabric pulls in more firmly against the body.
Step 17 — Cut and Mark the Back/Neckline Elastic
Add the two lengths together (73.1 + 45.9 = 119 cm) and cut one continuous piece of elastic. Mark the midpoint of the back section and the midpoint of the neckline section with a pin. Align these marks to the center of each corresponding edge before sewing. Begin and end the overlap at the shoulder seam area.
Step 18 — Attach and Topstitch Back/Neckline Elastic
Serge in place, then fold to the wrong side and topstitch as before. If you are not using foam cups, your swimsuit is now complete.
Step 19 — Insert the Foam Cups (Optional)
Slide each foam cup through the strap opening into the mesh pocket. The opening is just large enough to allow this without needing any additional finishing.
Choose cups in a neutral or skin-tone color. Dark cups can show through the fabric when the swimsuit is wet, even with dense fabric.
Care Instructions for Stretch Swimwear
Wearing
- Avoid contact with sunscreen and tanning oils while wearing — apply and allow to fully absorb into skin before putting the swimsuit on
- Do not use swimsuits with printed designs for intensive pool use — polymer prints crack under repeated chlorine exposure and friction
- Wash a new colored swimsuit separately before first use to check for color bleeding
Washing
- Hand wash or use a delicate machine cycle at low temperature (max 40°C / 104°F)
- Use a detergent designed for delicate or colored garments — avoid chlorine bleach
- Never wring out a one-piece swimsuit — gently squeeze the cups and press the main fabric between your palms
Drying
- Dry in shade or a well-ventilated room — avoid direct sunlight and heat sources
- Never iron stretch swimwear fabric — heat will damage the spandex and leave marks
- Dry flat or hanging — just make sure the garment is fully spread out
Storage
- Never store a damp swimsuit — mold can develop on the fabric and the damage is permanent
- Store foam cups in their natural rounded shape to maintain form
Shop Stretch Fabrics at KAHANNE Fabrics
Ready to start your swimsuit project? KAHANNE Fabrics carries single jersey, rib knit, and stretch fabrics perfect for swimwear, bodysuits, and activewear — shipped nationwide across the USA.