A triangle bikini is a timeless swimwear staple that's fun to sew and easy to personalize. Whether you're making it for a beach holiday, lounging by the pool, or relaxing on a tropical getaway, sewing your own bikini allows you to achieve a comfortable fit while choosing your favorite swim fabrics and colors.
The Winslet's Isla Triangle Bikini Sewing Pattern is a great choice for beginners looking to sew stylish swimwear. This easy-to-follow pattern features a classic triangle bikini top with adjustable tie strings and a seamless low-rise bikini bottom, making it a comfortable and versatile addition to your handmade wardrobe.
Why Sew a Triangle Bikini?
- Sew a classic two-piece swimsuit with a timeless silhouette.
- Enjoy adjustable halter neck and back ties for a customizable fit.
- Create a seamless low-rise bikini bottom for a smooth, comfortable finish.
- Experiment with different swim fabrics, colors, and prints to make a unique bikini set.
- Build confidence sewing stretch swim fabrics while creating practical handmade swimwear.
- Make a lightweight swimsuit that's perfect for beach vacations, pool days, and tropical holidays.
Why Choose the Winslet's Isla Triangle Bikini Sewing Pattern?
- Skill Level: Easy
- Design Features: Two-piece bikini featuring a classic triangle bikini top with adjustable tie-string halter neck and back ties, paired with a seamless low-rise bikini bottom.
- Available Sizes: US 02 - US 32 | UK 06 - UK 36 | EU 36 - EU 64
Supplies & Notions
You will need:
- Tape measure
- Chalk
- Fabric shears
- Pins
- Iron
- Sewing machine
- Sewing needles
- 3-ply polyester thread
- Thread cutter
- Serger (or use a zig-zag stitch as an alternative)
- Coverstitch machine (or use a twin needle or narrow zig-zag stitch as an alternative)
- 5 mm wide elastic
Always test your stitches on a fabric scrap before sewing the final garment.
Fabric Recommendations
Use lightweight 4-way stretch knit fabrics with 50–100% stretch, including:
- Nylon spandex scuba
- Polyester spandex jersey
- Tricot knit
- Ribbed swimwear knit
The sample garment is sewn using poly nylon lycra knit fabric, chosen for its:
- Smooth and stretchy finish
- Excellent flexibility and recovery
- Moisture-wicking and breathable properties
- Easy sewing with a stretch needle
Size Charts
Check the size charts and measure yourself to select the correct size, using the garment and body measurement tables in the guide.
Verify how much fabric you need by referencing the fabric yield table in the guide.
Pattern Inventory: What Pieces to Prepare
Prepare the following pattern pieces:
- A. Top — Cut 4 Fabric
- B. Front Bottom — Cut 2 Fabric
- C. Back Bottom — Cut 2 Fabric
- D. String — Cut 4 Fabric
For home printing, use the A4/US Letter pattern.
For copy shop printing, use the A0 pattern.
Pattern Marking
The pattern includes markings to help align and assemble both the bikini top and bottom accurately, including:
- Grainlines
- Seam allowances
- Center marking
- String casing
- Underbust
- Side seams
- Waist
- Leg openings
- Crotch markings
- Pattern piece identifiers (A, B, and C)
Transfer all markings carefully before sewing to ensure accurate construction.
Cutting Layout
Follow the cutting layout diagrams provided in the sewing guide to ensure each pattern piece is cut on grain.
The guide includes layouts for:
- 45" fabric width
- 60" fabric width
The layouts are non-directional. If your fabric has a nap or directional print, purchase additional fabric to accommodate pattern placement. The illustrated layouts use a US Size 12 for reference.
Fabric Cutting and Preparation
Arrange the pattern pieces according to the cutting layout diagrams, ensuring each grainline runs parallel to the fabric selvage.
If using fabric shears, trace the pattern pieces before cutting. Cut carefully outside any marking lines and clip all notches, as these help align the garment during assembly.
Transfer all pattern markings—including circles, buttonholes, and fold lines—to the wrong side of the fabric. Mark the center front on pieces cut on the fold to help align the garment accurately during construction.
Seam Allowance
Please follow the seam allowances as indicated on the pattern file layers. These are provided specifically for each piece to ensure accurate construction.
This pattern uses a 1 cm (or 3/8") seam allowance all around.
Step-by-Step Sewing Instructions
1. Create the Bikini Strings
1a. Fold the string piece in half lengthwise with the wrong side facing out. Press to crease the fold.
1b. Cut a piece of 5 mm wide elastic to match the length of the string. Place the elastic along the open long edge of the string and sew the open edges together with the elastic enclosed.
1c. Use a loop turner to turn the string right side out.
Repeat the same process for the second string piece.
1d. To create the third (longer) string, place two string pieces right sides together and sew the short edges together using a 1 cm (3/8") seam allowance, or overlock the edge. Open the seam and repeat Steps 1a–1c to complete the longer string.
2. Prepare the Triangle Bikini Top Panels
2a. Place two top pieces right sides together.
2b. Overlock the underbust, center, and side seams, leaving the casing area unstitched.
2c. Cut two pieces of 5 mm wide elastic, each matching the length of the center and side seam lines of the triangle bikini top. Position the elastic along the overlocked seam allowance on the wrong side, aligning its edge with the seamline, and stitch through the center of the elastic to secure it.
2d. Insert one of the shorter strings through the open string casing.
2e. Pull the string through the triangle top until it is aligned with the top edge, then overlock the top edge to secure the string in place.
2f. Turn the prepared bikini top panel right side out through the open string casing.
Repeat the same process for the remaining bikini top panel.
3. Sew the Bikini Top Casings
Fold the open casing seam allowances to the inside on both sides of each prepared bikini top panel and sew along the casing seamline to create the casings.
Repeat for the second bikini top panel.
4. Assemble the Bikini Top
Thread the longer string through the side casing of one bikini top panel and pull it out through the center casing. Then pass the same string through the center casing of the second bikini top panel, exiting through its side casing to complete the bikini top assembly.
5. Prepare the Bikini Bottom
5a. Place the front bottom pieces and their corresponding lining pieces right sides together. Align the waist and leg openings and pin.
5b. Overlock around the seamlines, leaving the side seams and crotch unstitched.
5c. Repeat the same steps for the back bottom pieces and their lining.
6. Add Elastic to the Bottom
6a. Cut three pieces of 5 mm wide elastic, each matching the length of the waist and leg openings. Position the elastic along the overlocked seam allowance on the wrong side of the leg openings and waist, aligning the elastic edge with the seamline. Stitch through the center of the elastic to secure it.
6b. Repeat the same process for the back bottom panel.
7. Join the Front and Back Bottom
7a. Turn the prepared back bottom right side out and press. Insert the back bottom through one of the open side seams of the prepared front bottom. Align the outer front with the outer back, and the inner front with the inner back.
7b. Align the crotch and side seams, then overlock to join them.
8. Turn the Bikini Bottom Right Side Out
8a. Carefully remove 1–2 inches of the overlock stitching at the waist near one of the side seams.
8b. Pull the back bottom through the opening. Arrange the front pieces right sides together and the back pieces right sides together to create the seamless bikini bottom.
9. Finish the Waist Opening
Fold the seam allowance to the inside and close the opening neatly using a hand blind stitch to complete the seamless finish.
Ready to Sew Your Own Triangle Bikini?
A triangle bikini is a rewarding project that combines simple construction with a timeless design. Featuring an adjustable tie-string halter top and a seamless low-rise bottom, the Isla Triangle Bikini Sewing Pattern is perfect for creating comfortable, custom-fit swimwear you'll love wearing.
Whether you choose classic solid swim fabric or a vibrant print, this easy-level sewing pattern includes detailed instructions to guide you through every step of the process. Download the pattern today and sew a handmade bikini that's ready for your next beach day or poolside getaway.
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Browse our Swimwear Sewing Pattern Collection for more stylish handmade swimsuits, bikinis, swim dresses, and beachwear patterns perfect for sunny days and tropical vacations.
Join the Community & Get Support
Share your finished Isla Triangle Bikini on social media with #MadeWithWinslets. If you have questions, feedback, or customization requests, contact the Winslet's team at support@winslets.com.
