What Is Swimsuit Material?

If you’ve ever wondered what the heck swimsuits are made of, you’re not alone. Like many other athletic or performance items in our closets, the materials contained in swimsuits aren’t always immediately apparent.

But these days, we’re all asking a lot more questions about our clothing: How and where it’s made, under what conditions, with what materials, and how sustainable are they? It’s certainly a tightrope walk to find products that successfully marry the performance and longevity we need with more ethical considerations. Swimsuits definitely fall in the category of ‘room for improvement.’ 

But let’s go back in history to gather the full story:

Swimwear Fabrics in History

It was in the 18th Century that public bathing became popular, and modesty necessitated the invention of some kind of garment. Before that, bathing was done in private and mostly nude.

The first true swimsuit was, in all earnest, a dress. Known as “bathing costumes,” these garments were made of wool, canvas, or flannel and even featured sleeves. They were even worn with socks. Suffice to say; there weren’t many speed records being set in those ensembles!

According to this article on Google Arts & Culture:

“Some gowns even had weighted hems to prevent the fabric from riding up mid-swim, saving women from suffering the embarrassment of unwittingly showing some leg. Swimming was deemed a healthy pursuit, but it sure couldn’t have been any fun in those suits.”

Those early dresses evolved into bloomers (controversial at the time because only men wore pants.) The priority was clearly modesty over performance. 

It was sports that provided the impetus. Around the 1896 Olympics, swimsuits changed drastically. For the first time, swimming was seen as a sport, and one-piece swimwear designed for movement and speed in the water took priority over modesty. These suits were cut more closely to the body and made use of the newest materials, like sleek nylon.

What started as ‘performance’ soon became fashion. As these garments made their way to consumers, design elements were added. Colors, cuts, frills, and shaped necklines all helped you stand out on the beach or by the pool. But, it was the bikini that really shook up the status quo. They emerged around 1946, designed by Louis Réard. 

Like all athletic clothing, there were ongoing innovations in materials and cuts. While cotton twill was sometimes used, nylon proved popular due to its stretch, lightness, and durability in the water.

Material innovation has continued right up to the present day. Lycra, spandex, and elastane revolutionized all ‘stretchy’ clothes (from leggings to underwear and swimsuits), allowing us a ‘second skin’ like appearance that retained its shape when wet and proved more durable over multiple wears.

Most Popular Swimsuit Fabric Today

Today, most swimsuits are still manufactured from synthetic blends. Nylon and polyester are the most popular swimwear fabrics, though there are other bathing suit materials too. Knix swimsuits, for example, are made of primarily made of nylon (~85%) and spandex (~15%). You’ll find similar blends in swimwear fabric across most mainstream brands today. 

Let’s look a little more closely at those swimwear fabrics:

Nylon Swimsuits (or Nylon Blends)

Knix swimsuits are made of mostly nylon (blended with spandex), and it’s easy to see why this would be our first choice for swimsuit material. Nylon blends are water-resistant and quick-drying, which makes them an almost perfect bathing suit material.

This swimsuit fabric has a slight sheen, which makes it attractive when styled into a swimsuit. And, when mixed with a stretch material, it can be wonderfully figure-hugging and even slightly compressive, which is ideal for those who want a ‘gentle hug’ of support.

On the downside: Nylon is not quite as UV resistant as polyester. Also, like all synthetic fabrics, nylon fabric takes a toll on the environment both when it’s manufactured and as it goes through its life cycle and degrades.

Polyester Swimsuits (or Polyester Blends)

Polyester, either on its own or as a blend with something that adds ‘stretch,’ is another popular fabric for bathing suits. The polyester fabric holds its color and shape wonderfully and is exceptionally durable. It is also a lightweight swimwear fabric.

It also has resistance to chlorine and to UV rays, which makes it ideal for competitive swimsuits as well as beach suits. Polyester suits are also fast-drying, again making polyester ideal swimsuit material.

Polyester was once considered a scratchy kind of synthetic material, but modern blends are smooth to touch, making it both comfortable and sleek in the water.

On the downside: Some polyester blends can be low quality (sometimes you really do get what you pay for, and cheap polyester suits can be a lot less durable than a well-made one with a stronger blend.) And, of course, being a synthetic material, polyester is not the most sustainable option for swimwear fabric.

PBT

Polybutylene Terephthalate, or PBT, is a plastic yarn fiber with natural stretch and recovery. It is part of the polyester family of fabrics. PBT has a natural stretch similar to Lycra and can be incorporated into sportswear, including swimsuit fabrics. Due to its chlorine resistance, it is commonly found in competitive swimwear. However, PBT is not considered environmentally friendly as it is a petroleum-based product.

ECONYL®

Introduced just in 2011, ECONYL® is regenerated nylon from pre and post-consumer products. According to Wikipedia, ECONYL® is made entirely from ocean and landfill waste, such as industrial plastic, fabric scraps from clothing manufacturing companies, old carpets, and "ghost nets" (lost or abandoned fishing nets.)

While certainly a step in the right direction in transforming single-use plastics into reusable products, it is worth noting that due to its material makeup, using ECONYL®  in bathing suits or other garments will still contribute to microplastics as it breaks down.

Specialty Swimwear Fabric: Period Swimwear

Period swimwear (also known as leakproof swimwear or period-proof swimwear) is a relatively new offering. Basically, it leverages the same technology as period underwear with some added secret protection to make it work in water.

The best part? Just like period underwear, period swimwear looks just like regular swimwear and comes in a variety of styles, from bikini bottoms to one-pieces. You’ll even have a choice of color!

So how exactly does Knix period swimwear work? The layers in the gusset of a leakproof swimsuit work to trap and absorb your period, so it doesn't leak in the water (or on land!) Our Swimwear features the same Leakproof Technology as our Period Underwear with an additional thin layer of waterproof material for extra protection.

The inner layers absorb the blood and trap it, so there's no leakage when you swim. When it goes in the laundry with detergent, it releases through the top layer— leaving your swim fresh and clean for tomorrow's laps.

Knix Leakproof Swimwear has a super discreet absorbent pad in the gusset liner.

Sustainability Concerns

Clearly, swimwear is not the most environmentally friendly clothing category. Like all activewear (leggings, sports bras, etc.), the performance requirements for swimwear are best served by synthetic materials. This means that the best swimsuit fabric for performance may not always be the best fabric for the environment.

Of course, there are considerable sustainability concerns about how these clothes are manufactured and treated throughout their lifespan. As we learn more about microplastics, it becomes clear that future innovations are required to deliver products that stand up to our performance requirements and offer more sustainable solutions.

Until those materials and solutions are developed, here are some things you can prioritize to better care for the environment:

• Avoid single-use plastics: If you want to tackle the plastics in your environment, single-use plastics are the best place to start. These items are used once and immediately discarded. Consider reducing or eliminating:
• Plastic bags (swap them for reusable bags)
• Plastic drink containers (instead, BYOB)
• Plastic straws and cutlery
• Plastic water bottles 
• Q-tips, plastic razors, toothbrushes, etc.
• Sort and separate your garbage properly
• Do not launder your clothes more than you need to
• Avoid beauty and cosmetic products with microbeads

Natural Swimsuit Materials

You may encounter swimsuits made of natural fibers, or blends of natural fibers, like:

• Hemp
• Cotton
• Bamboo

Again, while certainly a step in the right direction, these materials also lack a lot of the characteristics that people demand in swimsuits today.  The perfectly ideal fabric is just not yet clear.

Suffice it to say, we are all working hard to find better options, but we simply haven’t found the best fabric from both an environmental and a performance standpoint yet…

What to Look for in a Swimming Suit in 2023

But you need a swimsuit NOW… So when you’re shopping, what should you look for? While it’s always a good idea to check the label to see what materials you’re dealing with, these are the most important things to prioritize when you’re shopping.

1. Look and Feel

First and foremost, don’t buy a swimsuit or bikini that you don’t like the look of. You deserve nothing less than a swimsuit that makes you feel confident and beautiful. 

That means you should feel it enhances all the parts you love the most and helps minimize any body parts you feel discomfort about (of course, we’d absolutely prefer it if there were no body parts that you felt discomfort about!)

But beyond the look, you should feel good in it too. That means supported the way you want to be, ‘held in’ if that’s the feeling you want, free to move and jump and run in it. There shouldn’t be any bits that dig in uncomfortably or straps that slip. You shouldn’t be constantly distracted by your swimsuit. It should simply be there, doing its job, while you enjoy yourself.

2. Style Options

Within the Knix range, and beyond it to other brands of swimsuits, there are probably thousands of styles out there. 

• One-pieces, two-pieces, monokinis, rashguards, and more…
• Different necklines from high to plunging, sweetheart to V-neck. 
• Different bum coverage
• Wide straps, spaghetti straps, strapless
• Built-in bras swimsuits, underwire swimsuits
• Details like scallops, cutouts, ruching, power mesh, and even lace inserts
• Swimwear lining that gives you the coverage you want

Suffice it to say; you should be able to find the style or styles, you want. And if you’re completely overwhelmed by all the choices, you can never go wrong with a classic maillot style. It is, simply put, the little black dress of the swimsuit world. 

3. Size Range

Never, ever compromise on the right size. That means a swimsuit that fits just right. No uncomfortable seams or straps digging in. Or straps that fall down. The swimsuit should make you feel gently held in and supported. Your bust shouldn’t spill out.

The right fit means a wide range of sizes to suit every body. Knix swimsuits come in sizes from XS to XXXXL and a number of different styles that will flatter different shapes and silhouettes. There’s a stylish, chic option for every kind of body and design taste.

4. Color Options & Colorfast

Any material that’s going to go in the water needs to be colorfast. That’s why synthetics are so great for swimsuits—they generally hold their color and withstand the elements, like sun, saltwater, and chlorine.

You should also be able to find a range of colors to suit your mood, taste, and seasonal trends. Color is a great way to shake up a basic suit. You can even mix and match tops and bottoms in different colors. Have fun, get playful, and don’t be afraid to try something you wouldn’t normally wear. 

5. Period / Leakproof Swimwear

If you’ll be swimming or vacationing while on your period, it’s good to consider period swimwear. Period swimwear is a relatively new option on the market, but it’s worth considering!

Period swimsuits will absorb period blood. But it can also absorb sweat or urine (light bladder leaks.) So if you suffer from urinary incontinence, whether temporary or persistent, this is a great product to give you some freedom and confidence. 

Period swimwear is designed to look just like regular swimwear. Across brands, it comes in many different styles and colors. You can find:

• Two-piece swimsuits or one-piece period swimwear bottoms
• A variety of colors and patterns
• Simple maillot-style swimsuit, or ones with details like ruching, cut-outs, or wraparound
• Bikini bottoms that are classic bikini style, high-rise or boyshorts style
• Swimsuits with other details like built-in shelf bras
• And so much more…

Basically, there’s something for everyone. And nobody will know the difference between your period swimsuit and any other swimsuit you might pick. Indeed, you might find yourself reaching for your period swimsuit even when you don’t have your period (which is great for those with irregular periods too.)

6. UV Protection (UPF)

If protection from the sun is a top concern (and it should be!), it’s worth checking to make sure your swimsuit has an Ultraviolet Protection Factor (UPF) rating. While any additional layer will offer some degree of sun protection, clothing with a UPF is tested according to strict guidelines. Ultraviolet Protection Factors of 50 or more represent excellent protection.

It’s worth noting that UPF clothing with built-in UV protection extends beyond swimwear and rash guards. You can also find UPF t-shirts, leggings, and more…

However, it’s important to note that you still need to wear sunscreen on the parts of your body not protected by the UPF fabrics, including the face, hands, and legs. Pay special attention too to the neckline, back, and any parts of your decollete that may be exposed to the sun around the straps of your swimsuit. And don’t forget to reapply sunscreen throughout the day, especially after you’ve been in the water.

7. Quick-Drying

Another bonus of those common swimsuit materials like polyester and nylon is that they are quick-drying. This allows you to dry off quickly between dips while lounging poolside or on the beach. It also means your swimsuit will dry quickly after a handwash, which means you can give it a proper rinse after a day in the water. This will remove chlorine, sand, and residue from sunscreen. If you’re wearing period underwear, it’s important to wash it after each wear to ensure it can be re-worn.

8. Stretch/Elasticity

Most swimsuits today are made of some blend of nylon or polyester and ‘stretch’ materials. But that doesn’t mean they all have the same amount of stretch or compression. Check the labels, but also try on the swimsuit. Move around in it—does it move with you? Read reviews—do reviewers say it gets baggy after a few wears?

Just like leggings, cheaper swimsuits can get baggy quickly. So think about investing a little more to get a higher-quality swimsuit. Then do your part to prolong its lifespan. Lay it flat to dry, so it isn’t stretching out. Alternate a few swimsuits, so they have a ‘rest period’ between wears.

9. Easy to Care for

This is a rule for almost any garment: Check the care instructions. Most swimsuits should be a simple hand wash/rinse, followed by an instruction to lay flat to dry. Anything more complex might become too much of a chore (especially when you’re supposed to be enjoying a vacation.)

But ease of care isn’t just about laundry instructions. Swimsuits in darker colors or patterns will always be more forgiving of any stains/spills. Keeping a white swimsuit pristine may not be practical (though they do look fantastic!)

10. Sustainability / Longevity

While we don’t yet have a perfect solution for a sustainable swimsuit, one thing you can do is invest in a swimsuit that will last for longer. Cheap clothing that gets discarded after a short season does significantly more damage to the environment. A classic and flattering swimsuit that will last you many more seasons is a choice that has more longevity and, therefore, reduces the turnover of waste.

Discover the Best Knix Swimsuit You!

Now you know what to look for in your ideal swimsuit, let’s look at some recommendations from the Knix swimwear range!

Best for Bust Support: Sculpt One Piece or Bikini Top

The Sculpt Bikini Top: A retro-styled bikini top with built-in foam cups for the ultimate shape and support. Plus, removable straps for a bandeau look (hello, tan-line free tan!)

How it Fits:

Medium coverage bottom. Removable straps and adjustable back closure.

Size Options: XS to XXXXL

Best for Sports & Activities: High Energy One-Piece

The High Energy One Piece is a sleek suit that features a chunky front zipper, a high neck, and a racer back for maximum range of motion. Mesh sides create interesting style lines while also giving you good support.

How it Fits:

Slightly higher cut on thigh and bum.

Size Options: XS to XXXXL

Best for Period Protection: Leakproof Classic One Piece

This is like a little black dress in swimsuit form. You can’t go wrong with this swimsuit. The Leakproof Classic One Piece in Black has a hidden shelf bra for support, and its clean, classic lines are universally flattering.

How it Fits: 

Smooth fit over the body with medium bum coverage. It is fully lined with a no-dig leg opening, a built-in inner bra for support, and adjustable straps. It comes in extended sizes that support bigger cups.

Size Options: XS to XXXXL

Best for Tummy Control: Ultra High Rise Bikini Swim Bottom

The Ultra High Bikini Bottom is a trendy ultra-high waist bottom that hits above the natural waistline and features ultra-flattering side seams for a gently gathered look.

How it Fits:

Silhouette is cut moderately on the leg and bum, and a no-dig leg opening. Fully lined.

Size Options: XS to XXXXL

Shop the full range here.

We hope you found this post informative — but remember: we’re not doctors and this post is not medical advice! While all posts are fact-checked and well researched, we always recommend you chat with your doctor about any questions or concerns you might have regarding a medical condition. We’re here to support and educate, but never with the aim of disregarding professional medical advice you’ve been given. Phew, now that that’s out of the way, you can go on living unapologetically free.