Bathing Suit Thread: Ultimate Guide to Durable Swimwear Construction

1. Introduction: Why Thread Choice Makes or Breaks Swimwear

Ever experienced the heartbreak of a swimsuit seam popping mid-swim? It’s not just embarrassing—it’s a reminder that the tiniest details, like thread choice, can make or break your swimwear. Bathing suits face a relentless assault from chlorine, saltwater, and UV rays, demanding more from your materials than almost any other garment. That’s why selecting the right thread isn’t just a technicality—it’s the foundation of durable, comfortable swimwear.

In this guide, we’ll dive into the science and strategy behind choosing the best bathing suit thread, explore essential sewing techniques, and troubleshoot common pitfalls. Whether you’re a seasoned pro or a first-time swimwear maker, mastering these details will help your creations survive countless summers. Let’s unravel the secrets to swimwear that stays strong, stylish, and secure—no matter how wild the waves get.

Table of Contents

• 1. Introduction: Why Thread Choice Makes or Breaks Swimwear
• 2. Best Thread Types for Swimwear: Polyester vs. Nylon Showdown
• 3. Swimwear Sewing Techniques: Stitches, Needles & Tension Mastery
• 4. Material Comparison: Choosing Threads for Swimwear Components
• 5. Essential Tools: Handling Slippery Swim Fabrics Like a Pro
• 6. Troubleshooting Common Swimwear Sewing Disasters
• 7. Lining & Support Systems: Hidden Structure Secrets
• 8. Conclusion: Building Swimwear That Survives Summer
• 9. FAQ: Swimwear Thread Questions Answered

2. Best Thread Types for Swimwear: Polyester vs. Nylon Showdown

Choosing the right thread for your bathing suit isn’t just about color matching—it’s about engineering seams that stand up to the harshest pool and beach conditions. Let’s break down why polyester dominates, where nylon falls short, and when specialty threads are worth the investment.

2.1 Why Polyester Reigns Supreme: Chlorine & UV Resistance

Imagine your swimsuit spending hours basking in the sun, soaking in salty waves, or braving chlorinated pools. Polyester thread is built for this challenge. Industry leaders like Modak Knits and Sailrite consistently recommend polyester as the gold standard for swimwear construction—and here’s why:

• Chlorine Resistance: Polyester outperforms nylon, resisting the chemical onslaught of pool water and preventing premature seam failure.
• UV Protection: Unlike nylon, polyester stands strong under relentless sun, maintaining its strength and color much longer.
• Saltwater Tolerance: Polyester shrugs off salt, keeping seams intact and colors vibrant.

Research confirms that polyester thread maintains over 90% of its strength after repeated chlorine exposure, while nylon quickly degrades. Sailrite notes, “Polyester thread is known for its strength, durability, and low shrinkage and stretch. It’s the most common thread for outdoor applications.” In other words, it’s like giving your swimsuit a suit of armor.

Visualize this: If you could watch a time-lapse of two swimsuits—one stitched with polyester, the other with nylon—after a season in the pool, the polyester seams would still look crisp and strong, while the nylon might appear frayed, faded, or even broken.

For most swimwear projects, especially those destined for heavy pool or sun use, UV-treated polyester thread is the clear winner.

2.2 Nylon's Limitations: The Hidden Vulnerability

Nylon thread has its fans, especially for its initial strength and soft, stretchy feel. But when it comes to swimwear, nylon hides a fatal flaw: it’s highly vulnerable to chlorine and UV rays.

• Chlorine Sensitivity: Nylon’s chemical structure breaks down quickly in chlorinated water, leading to weakened seams and potential wardrobe malfunctions.
• UV Degradation: The Thread Exchange and other sources highlight nylon’s rapid loss of strength and color under sunlight, making it unsuitable for long-term outdoor exposure.

Imagine examining nylon thread under a microscope before and after a summer of swims—those once-smooth fibers become rough, brittle, and faded, a stark contrast to polyester’s resilience. While nylon may be tempting for fashion swimwear or delicate fabrics, it’s a risky choice for any suit that will see regular pool or sun time.

2.3 Specialty Options: When to Consider PTFE or Woolly Nylon

Sometimes, swimwear demands even more than polyester can offer. Enter specialty threads:

• PTFE Thread (e.g., Tenara®): This premium option is virtually immune to UV, chlorine, saltwater, and even harsh cleaning agents. It’s the “lifetime thread” of the industry—ideal for extreme conditions or professional-grade suits. The trade-off? PTFE is more expensive and can be trickier to sew, sometimes requiring machine adjustments or specialized needles.
• Woolly Nylon: For soft, stretchy seams—especially finishing edges or hems—woolly nylon shines. Its fluffy, textured structure delivers comfort against the skin and exceptional elasticity. However, it’s best reserved for overlock or serger machines and isn’t suitable for high-stress structural seams.

Cost vs. Benefit: While PTFE threads offer unmatched durability, most home sewists and small manufacturers find UV-treated polyester delivers the best balance of performance and practicality. Woolly nylon is a comfort upgrade for edges, but polyester remains the backbone of strong, lasting swimwear seams.

3. Swimwear Sewing Techniques: Stitches, Needles & Tension Mastery

Thread choice and having the best sewing machine for embroidery and sewing are just the beginning. The way you sew your swimsuit—stitch selection, needle type, and tension settings—determines whether your seams stretch, recover, and endure the rigors of summer fun. Let’s break down the techniques that set professional swimwear apart.

3.1 Stitch Types That Survive Stretching: Zigzag vs. Lightning Bolt

Swimwear needs seams that stretch as much as the fabric itself. Here’s what the experts recommend:

• Zigzag Stitch: The classic choice for domestic machines. A wide and short zigzag (around 3.0–4.0mm width, 1.5–2.0mm length) allows seams to flex without breaking. Perfect for side seams, hems, and attaching elastic.
• Three-Step Zigzag (Multi-Step Zigzag): The secret weapon for elastic. This stitch makes three small zigzags per cycle, distributing tension evenly and preventing "popped stitches"—especially around leg openings and armholes. Recommended settings: 5.0mm width, 1.5mm length.
• Stretch Stitch (Lightning Bolt): For structural seams, the lightning bolt stitch offers maximum stretch and recovery, ideal for high-movement areas.

Pro Tip: Always test your chosen stitch on scrap fabric—then stretch it to see if it holds up. A seam that can stretch from 4 to 6 inches (a 50% increase) without breaking is your goal.

3.2 Needle Selection: Microtex vs. Ballpoint for Delicate Fabrics

The wrong needle can turn your swimwear dreams into a nightmare of skipped stitches and fabric snags. Here’s how to get it right:

• Microtex Needles: Fine and sharp, these needles penetrate lycra and spandex blends cleanly, minimizing fabric damage. SCHMETZ recommends Microtex for precise work, especially with delicate or laminated fabrics.
• Ballpoint/Stretch Needles: Designed to slide between knit fibers, ballpoint and stretch needles prevent snags and skipped stitches. For dense swim fabrics, stretch needles are often the safest bet.

Test, test, test: Try both types on your chosen fabric. Skipped stitches or visible holes? Switch needles until you find the perfect match.

3.3 Tension Troubleshooting: The 50% Stretch Test Protocol

Perfect tension is the unsung hero of swimwear sewing. Too tight, and your seams will pucker or snap; too loose, and they’ll sag or unravel. Here’s a foolproof protocol:

1. Create a Test Sample: Cut a 2" x 6" strip of your swim fabric.
2. Sew a Test Seam: Use your chosen thread, stitch, and needle.
3. Mark 4" Along the Seam: This is your reference length.
4. Stretch to 6": (50% stretch) and check for:
   • Seam breakage
   • Fabric distortion
   • Smooth recovery when released

If your seam passes the test, you’re ready to sew with confidence. If not, adjust tension, stitch length, or needle type and try again. Remember, saltwater and chlorine can accentuate tension issues over time, so err on the side of flexibility.

By mastering these thread choices and sewing techniques, you’ll create swimwear that’s not only stylish but built to last—through every splash, dive, and sun-soaked adventure. Ready to stitch your best suit yet?

4. Material Comparison: Choosing Threads for Swimwear Components

When it comes to constructing swimwear that stands up to sun, salt, and chlorine, not all threads are created equal. The right thread for each part of your suit can mean the difference between a wardrobe malfunction and a suit that lasts season after season. Let’s break down the best options for every component—seams, fashion details, and those all-important finishing touches.

4.1 Structural Seams: Why Polyester Dominates

Imagine the side seam of your favorite swimsuit—bearing the brunt of every dive, stretch, and twist. This is where polyester thread truly shines. Industry stress tests and professional recommendations consistently point to Tex 40 polyester as the gold standard for main seams in swimwear. Why?

• Unmatched Strength: Polyester’s high tensile strength means it resists breakage even under vigorous movement.
• Chlorine & UV Resistance: Unlike nylon, polyester maintains integrity after repeated exposure to pool chemicals and sunlight. This translates to seams that don’t degrade or pop after a few swims.
• Abrasion Resistance: Polyester shrugs off friction from sand, surf, and washing, keeping seams intact.

In side-by-side stress tests, polyester outperforms nylon, especially after exposure to chlorinated water. While nylon may start strong, it rapidly loses strength—leading to seam failures just when you need them most. If you want your suit to survive the summer (and beyond), polyester is the thread to trust for all structural seams.

4.2 Fashion vs. Performance: Nylon's Niche in Designer Swimsuits

Nylon thread isn’t without its charms. On the runway and in high-fashion swimwear, nylon is often chosen for its:

• Superior Drape: Nylon’s softness and flexibility allow designers to create suits with elegant lines and fluid movement.
• Skin Comfort: Its silky texture feels luxurious against the skin, making it a favorite for delicate, limited-use garments.

But there’s a catch: nylon’s Achilles’ heel is its vulnerability to chlorine and UV rays. Over time, colors fade and seams weaken—a dealbreaker for active or frequently worn swimwear. Designers may opt for nylon in statement pieces meant for special occasions or photo shoots, but for daily wear, its limitations become clear. As one designer put it, “Nylon is perfect for the catwalk, but polyester is for the pool.”

4.3 Finishing Touches: Woolly Nylon for Comfort Edges

Ever wondered how some swimsuits feel buttery-soft at the edges, never chafing or digging in? The secret is often woolly nylon thread, especially when used in serger loopers or the bobbin case.

• Superior Elasticity: Woolly nylon expands and contracts with every move, making it ideal for hems and edges that need to stretch.
• Chafe-Free Comfort: Its fluffy, textured structure creates a gentle finish—no more scratchy seams.
• Professional Finish: Woolly nylon “fills in” between stitches, giving hems a smooth, bulk-free look.

For best results, use woolly nylon in the upper and lower loopers of your serger, or in the bobbin case of a regular machine. It’s not designed for main seams, but for those finishing touches—leg openings, necklines, and armholes—it’s a game-changer. If you’re sewing with foam-backed fabrics, adjust your serger settings for optimal stretch and recovery.

Summary Table: Thread Choices for Swimwear Components

By matching your thread to each part of the suit, you’ll create swimwear that’s not just beautiful, but built to last.

5. Essential Tools: Handling Slippery Swim Fabrics Like a Pro

Sewing swimwear is a bit like wrestling a slick, stretchy eel—unless you have the right tools. From cutting to securing and hooping, these accessories will transform your process from frustrating to flawless.

5.1 Cutting Solutions: Rotary Tools vs. Micro-serrated Scissors

If you’ve ever tried to cut swim fabric with regular scissors, you know the struggle—shifting, stretching, and jagged edges. Enter the rotary cutter:

• Speed & Precision: Rotary cutters, paired with a non-slip mat and pattern weights, allow you to slice through slippery fabric up to 70% faster than traditional scissors.
• No Distortion: The rolling blade glides smoothly, preventing the “walking” effect that can distort stretch fabrics.
• Pattern Placement: Cutting with the printed side up and using weights ensures your motifs land exactly where you want them.

While micro-serrated scissors can work in a pinch, nothing beats the efficiency and accuracy of a sharp rotary cutter for swimwear projects.

5.2 Fabric Securing: Why Clips Trump Pins Every Time

Pins and swim fabric? A recipe for snags, holes, and frustration. That’s why stainless-steel clips are the pro’s choice:

• No Snags: Magnified images show how pins can damage delicate knits, while clips leave fabrics pristine.
• Even Tension: Clips hold layers together without distortion, making it easier to sew smooth, even seams.
• Swimsuit-Flipping Prevention: Use clips to secure tricky curves and prevent layers from shifting as you sew.

Pattern weights are also a lifesaver during cutting—think of them as your silent sewing assistants, keeping everything in place while you work.

5.3 Hooping Stations: Precision Workflow Integration

For those tackling garment embroidery on swimwear using a hoopmaster hooping station, precision is everything. That’s where the MaggieFrame HoopTalent station steps in:

• Consistent Alignment: The HoopTalent station ensures every suit is hooped in exactly the right spot, batch after batch.
• Time Savings: Users report up to 50% faster elastic application and garment preparation, freeing you up for more creative work.
• Professional Results: By minimizing fabric distortion and maximizing repeatability, the MaggieFrame system delivers crisp, professional embroidery—every time.

Whether you’re a solo sewist or running a busy studio, integrating a hooping station into your workflow can revolutionize your swimwear production.

6. Troubleshooting Common Swimwear Sewing Disasters

Even seasoned sewists encounter swimwear mishaps—skipped stitches, fabric runs, elastic woes. But don’t worry: with the right fixes, you’ll turn disasters into triumphs.

6.1 Skipped Stitches: Silicone Spray Fix for Rubber Elastic

Skipped stitches are the bane of swimwear sewing, especially when stitching over rubber elastic. Here’s how to banish them:

• Needle Know-How: Always use a fresh ballpoint or stretch needle (size 70/10 or 80/12). Dull or universal needles are a recipe for trouble.
• Rethread Everything: If stitches skip, rethread both top and bobbin—sometimes the culprit is a missed tension disc.
• Silicone Hack: For rubber elastic, lightly swipe a silicone-treated cotton swab along the elastic before sewing. This reduces friction and helps the needle glide through.
• Thread Quality: Stick with high-quality polyester thread; low-grade options can cause skips even with the right needle.

As seen in the “4 Reasons You’re Getting Skipped Stitches” video, these simple steps solve most issues—saving your sanity and your seams.

6.2 Fabric Damage Prevention: Walking Feet & Tension Mods

Swim fabrics are delicate, and the wrong approach can leave you with runs, holes, or even burnt spots. Here’s how to keep your suit flawless:

• Presser Foot Power: A walking foot feeds both layers evenly, preventing shifting and puckering—especially on lycra and spandex blends.
• Needle Selection: Microtex or ballpoint needles minimize snags; always match needle size to fabric weight.
• Tension Tune-Up: Too much tension can cause puckering or even melt synthetic fibers. Adjust for a smooth, flat seam.
• Overheating Checklist: Slow down your sewing speed and change needles regularly to avoid heat buildup and material damage.

By prepping your machine and fabric, you’ll sidestep the most common causes of swimwear carnage.

6.3 Elastic Application: The 25% Stretch Rule Demystified

Getting elastic just right is part art, part science. Here’s the secret:

• Pattern Marking: Divide both elastic and fabric into quarters, then match marks for even distribution.
• The 25% Rule: Cut elastic about 25% shorter than the opening—stretch the elastic (not the fabric) as you sew for perfect gathers.
• Three-Step Zigzag: Use a wide, multi-step zigzag stitch to secure elastic, allowing maximum stretch and recovery.
• Curve Awareness: Pay attention to inside (back) vs. outside (front) curves—tension may need slight adjustments to prevent puckering or loose edges.

Slow-motion tutorials show how this method creates snug, comfortable edges that won’t bag out or dig in.

By mastering these materials, tools, and troubleshooting techniques, you’ll elevate your swimwear from homemade to high-performance—ready to make a splash, no matter what the summer throws your way.

7. Lining & Support Systems: Hidden Structure Secrets

Swimwear isn’t just about bold prints and sleek silhouettes—what’s underneath truly counts. The right lining and support systems transform a simple suit into a second skin, offering comfort, coverage, and confidence whether you’re catching waves or lounging poolside. Let’s peel back the layers and reveal the secrets to swimwear that fits and flatters, no matter the body or activity.

7.1 Lining Fabric Compatibility: Stretch-Matching Essentials

Choosing the perfect lining for your bathing suit is a balancing act—think of it as pairing dance partners who need to move in perfect sync. The lining must match the stretch and recovery of your outer fabric, or you risk sagging, drooping, or uncomfortable bunching once your suit gets wet.

Key Properties to Consider:

• Stretch Compatibility: Lining should have a similar percentage of stretch as your main fabric. If the lining is less stretchy, it can “hold back” the outer layer, causing it to sag or separate—especially when wet.
• GSM (Grams per Square Meter): Heavier linings (higher GSM) offer more support and opacity, while lighter ones provide a barely-there feel.
• Drying Time & Support: Polyester interlock linings are soft and stable but dry slower than nylon-spandex blends. Power mesh and power net linings offer targeted support but must be carefully matched to avoid separation issues.

Common Lining Fabrics:

Pro Tip: Always test how your lining and outer fabric behave together—especially when wet. A lining that’s too firm can leave your suit looking like a colorful Shar-Pei after a swim!

Opacity Check: Stretch both fabrics over your hand and run them under water. If you see too much skin, opt for a heavier or double-layer lining for modesty and comfort.

7.2 Foam Cups & Underwires: Chlorine-Resistant Options

Support in swimwear isn’t one-size-fits-all. Whether you want subtle shaping or serious lift, the right components make all the difference.

Foam Cups:

• Swim-Specific Foam: Look for medium-density foam cups finished with polyester lining inside and out. These are designed to resist chlorine and won’t soak up water like lingerie foam.
• Sizing: Available in a broad range, from size 12 to 32, to fit various bust shapes and support needs.
• Types: Standard foam cups for light support, molded cups for a firmer shape, and gel-filled cups for extra lift and shaping. All should feature non-serged edges to withstand water exposure.

Underwires:

• Not all swimsuits are underwire-friendly, but for those who crave extra support, underwired tankini tops or custom suits are an option. When integrating underwires, ensure your pattern allows for a full band and proper channeling—otherwise, stick to shelf bras or power mesh panels for structure.

Waterlogging Warning: Only use foam cups and underwires labeled for swimwear. Lingerie materials can absorb water, leading to discomfort and sagging.

7.3 Seam Engineering: Flatlock vs. French Seam Showdown

Seams are the unsung heroes of swimwear comfort and durability. The wrong seam can chafe, unravel, or even corrode in saltwater—so let’s break down the best options:

• Flatlock Seams: These low-profile seams lie flat against the skin, reducing bulk and virtually eliminating chafing. Created with a serger or zigzag stitch, they’re perfect for active swimwear and sensitive skin.
• French Seams: Fully enclosed seams that hide raw edges, best suited for lightweight swim fabrics. They offer a neat finish but may add bulk if used on thicker materials.
• Felled & Overlocked Seams: Felled seams fold one allowance over the other for strength—great for high-stress areas. Overlocked seams trim and stitch simultaneously, ideal for stretch fabrics and preventing fraying.

Chafing Tests: Sensitive skin? Flatlock seams are your friend. For extra insurance, use seam tape to finish internal edges and keep everything smooth.

Saltwater Survival: Over time, saltwater can corrode poorly finished seams. Regularly inspect for wear, and choose polyester thread for maximum resistance.

8. Conclusion: Building Swimwear That Survives Summer

Choosing the right bathing suit thread and mastering swimwear construction isn’t just technical—it’s transformative. Polyester thread stands tall for its unbeatable strength and resilience, while stretch stitches and the right needles ensure every seam moves with you, not against you. Don’t forget: matching your lining stretch, using swim-specific foam cups, and engineering chafe-free seams are the hidden secrets to suits that last.

Ready to dive in? Here’s your quick-reference checklist:

• Use UV- and chlorine-resistant polyester thread for all main seams.
• Match lining stretch to your outer fabric—test for sagging or separation.
• Choose swim-specific foam cups and underwires for lasting support.
• Opt for flatlock or overlocked seams to prevent chafing and wear.
• Always test your stitches, tension, and fit before the final sew.

With these strategies, your custom swimwear will outlast the hottest summer days—leaving you free to focus on fun, not failures. Now, go make a splash!

9. FAQ: Swimwear Thread Questions Answered

9.1 Q: Should I pre-wash my swimwear thread before sewing?

A: Pre-washing is generally not necessary for high-quality polyester or nylon thread, as these are designed to resist shrinkage and color bleeding. However, if you’re concerned about dye transfer or are using a specialty thread, testing a small sample is always wise.

9.2 Q: Can I sew swimwear without a serger?

A: Absolutely! While a serger provides professional-looking, stretchy seams, a regular sewing machine with a zigzag or stretch stitch and polyester thread will do the trick. Just be sure to test your settings on scraps for best results.

9.3 Q: How do I repair a popped seam in my swimsuit?

A: Use a stretch or ballpoint needle and polyester thread to restitch the seam with a zigzag or triple stretch stitch. Reinforce the area by backstitching at the start and end, and avoid pulling the fabric as you sew.

9.4 Q: Does thread type really affect UV protection in swimwear?

A: Yes—polyester thread offers superior UV resistance compared to nylon, helping maintain seam strength and color over time. For swimwear exposed to lots of sun, always choose UV-treated polyester thread for maximum durability.

With these answers and strategies, you’re equipped to tackle any swimwear sewing challenge—thread, seam, and all!