Swimwear Fabric Guide: Chlorine Resistance, UV Protection & Quick-Dry

The fabric inside a swimsuit matters more than the print on the outside. Nylon is soft and cheap but wears out fastest in chlorine. Polyester and polyester PBT blends resist chlorine and hold their shape far longer, making them the standard for competition and regular lap swimming. Specialty fibres such as Xtra Life Lycra add extra chlorine resistance to any blend, while UPF rated fabric adds genuine sun protection on top.

Most people choose swimwear based on cut, colour and price, and only think about fabric once a favourite suit has gone baggy, faded or started to smell no matter how often it is washed. Understanding what is actually in the fabric before you buy saves money and disappointment, particularly if you swim regularly rather than wearing swimwear a handful of times each summer. This guide breaks down the main fibres used in swimwear, what chlorine actually does to fabric, how UV protection is measured, and which combination suits different types of swimmers.

The Main Fabrics Used in Swimwear

Almost every swimsuit on the market is built from some combination of four fibres.

Nylon is the softest and lightest of the common swimwear fabrics, which is why it feels so comfortable against the skin. Its major weakness is chlorine. Repeated exposure breaks down nylon's molecular structure over time, causing the fabric to lose elasticity, fade and eventually thin out. A nylon spandex suit worn occasionally at the beach can last for years, but the same suit used for daily pool laps will noticeably degrade within a single swim season.

Polyester has a more chemically stable structure than nylon, which makes it naturally more resistant to chlorine, sunscreen oils and prolonged sun exposure. Polyester swimwear holds its colour and shape for far longer under regular pool use, though it is generally less stretchy than nylon unless blended with another fibre for give.

PBT, short for polybutylene terephthalate, is a textured polyester variant developed specifically for performance fabric. It offers stretch and recovery similar to spandex while remaining highly chlorine and heat resistant, which is why competition swimwear brands rely on it so heavily. A typical competition fabric blend runs around 80 percent polyester to 20 percent PBT, balancing chlorine resistance with the stretch needed for a snug, hydrodynamic fit.

Spandex, also called elastane or Lycra, is rarely used as a fabric on its own. Blended in at roughly 10 to 20 percent, it gives nylon or polyester the stretch and recovery that make swimwear fit snugly and move with the body. Standard spandex is the most chlorine sensitive fibre of the group, which is part of why manufacturers have developed chlorine resistant versions specifically for swimwear.

How Chlorine Actually Damages Swimwear

Chlorine works by oxidising organic material, which is exactly how it disinfects pool water. Unfortunately, the same oxidising process also attacks the molecular bonds in certain synthetic fibres, particularly standard spandex and nylon. Over repeated exposure this shows up as reduced stretch and recovery, fabric that feels thinner or more see through, and colours that fade faster than they would from sun exposure alone.

This is the exact problem that chlorine resistant fibre technologies were built to solve. Xtra Life Lycra, developed by The Lycra Company, is a spandex fibre engineered to resist degradation from chlorine, heat and sunscreen for up to ten times longer than untreated spandex. In live pool testing conducted by the fibre's manufacturer, fabric containing Xtra Life Lycra showed roughly 50 percent better chlorine resistance than the next best competing chlorine resistant elastane on the market. It has been used in swimwear since 2004 and is now common in both competitive and premium recreational suits.

UV Protection and the UPF Rating System

Swimwear fabric can also protect against sun exposure, and in Australia this is measured under the AS/NZS 4399 standard for sun protective clothing, first introduced in 1996 and most recently updated in 2020. The standard rates fabric using an Ultraviolet Protection Factor, or UPF, based on how much solar ultraviolet radiation it blocks.

The current classification system groups UPF ratings into three bands: a UPF of 15 is rated minimum protection, a UPF of 30 is rated good protection, and a UPF of 50 or 50+ is rated excellent protection, blocking 97.5 percent or more of UV radiation. Under the standard, 50+ is also the highest number a garment is permitted to display, even if it tests higher in the laboratory. Tighter, denser weaves generally block more UV than a loose or sheer knit, which is why a plain nylon spandex bikini typically carries a lower UPF than a densely woven rash guard or swim shirt in the same fabric family.

What Makes Swimwear Dry Quickly

Quick dry performance comes down to two things: how much water the fibre itself absorbs, and how tightly the fabric is woven or knitted. Polyester and PBT absorb very little water compared with natural fibres, so moisture sits on the surface rather than soaking into the fibre itself, which is part of why they dry noticeably faster than a cotton blend or a looser nylon knit. A tighter weave also helps water bead and run off rather than settling into the fabric, which is why densely constructed competition and technical swimwear tends to dry faster than a loosely knitted, fashion focused suit even when the fibre content is similar.

Sustainable Fabric Options

A growing share of swimwear is now made from ECONYL, a regenerated nylon developed by the Italian company Aquafil and launched in 2011. ECONYL is produced entirely from nylon waste, including reclaimed fishing nets, carpet offcuts and other landfill and ocean plastic, and is chemically identical to virgin nylon once regenerated, meaning it performs the same way in a finished garment. Producing ECONYL reduces the global warming impact of nylon by up to 80 percent compared with virgin, oil derived nylon, and brands including Speedo and Adidas now use it across parts of their swimwear ranges. For anyone wanting the softness and fit of nylon with a smaller environmental footprint, it is currently the most established option on the market.

Fabric Comparison at a Glance

Lining Fabric Matters Too

The outer fabric is not the only material doing work in a swimsuit. Many technical and competition suits use a separate PBT lining fabric behind the main panel, chosen specifically because it resists chlorine completely and holds its shape regardless of what the outer layer is made from. A common example is a 100 percent PBT stretch liner, used in high performance and club swimwear precisely because it will not lose elasticity or become see through with repeated chlorine exposure, even in areas of the suit under the most stress. If you are comparing two swimsuits with a similar outer fabric, checking whether one uses a proper PBT or chlorine resistant lining rather than a basic polyester or nylon lining is a good way to judge overall build quality.

Choosing Fabric for the Way You Actually Swim

The right fabric depends far more on how often you get in the water than on style preference. If you swim laps several times a week, a polyester or polyester PBT suit will noticeably outlast a nylon spandex equivalent, even though it may cost more upfront. If you mainly wear swimwear for beach days, sunbaking and the occasional swim, a nylon or nylon spandex blend offers better comfort and stretch without the durability trade off mattering as much.

If you are also comparing specific cuts and styles rather than just fabric, our women's swimwear guide and men's swimwear style guide cover how style and fabric work together for each. Fabric performance also matters more than usual for styles with extra structure or coverage, such as those covered in our plus size swimwear guide, since a firmer, higher spandex content fabric holds support panels in shape for longer under regular wear.

Sizing and Fabric Work Together

Even the best fabric will not perform well in the wrong size. A suit that is too tight stretches its recovery fibres further than intended every time it is worn, shortening its lifespan regardless of fabric quality, while a suit that is too loose will not hold its shape properly in the water. Our full guide on how underwear and swimwear sizing works explains how to measure yourself accurately so the fabric you have chosen actually gets to do its job.

Caring for Different Swimwear Fabrics

A few care habits make a genuine difference to how long any of these fabrics last. Rinse swimwear in cold water immediately after wearing it, whether in a pool or the ocean, to remove chlorine, salt and sunscreen residue before it has a chance to sit in the fibres. Hand wash in a mild detergent rather than a washing machine, which can stretch seams and damage support panels. Always skip the tumble dryer, since heat is one of the fastest ways to break down spandex and elastane regardless of how chlorine resistant the base fabric is. Lay swimwear flat in the shade to dry rather than in direct sun, which can fade colour over time even in fabric with a high UPF rating.

Common Mistakes to Avoid

• Assuming all spandex blends perform the same in chlorine, when chlorine resistant versions such as Xtra Life Lycra behave very differently to standard elastane

• Buying based on UPF alone without checking chlorine resistance, since a highly sun protective fabric is not automatically durable in a pool

• Machine washing or tumble drying swimwear regularly, which shortens the life of even the most chlorine resistant fabric

• Choosing fashion focused nylon swimwear for serious lap training, where a polyester or PBT blend will hold up far better

Frequently Asked Questions

What is the most chlorine resistant swimwear fabric?

Polyester and polyester PBT blends are the most chlorine resistant fabrics commonly used in swimwear, which is why they are the standard choice for competition and daily lap swimming. Chlorine resistant spandex fibres such as Xtra Life Lycra also significantly improve the durability of stretch blends compared with standard elastane.

Does a high UPF rating mean the fabric is also chlorine resistant?

Not necessarily. UPF measures how much UV radiation a fabric blocks, while chlorine resistance depends on the specific fibres used. A fabric can have excellent sun protection and still degrade quickly in a chlorinated pool if it is made mostly from standard nylon or untreated spandex.

Is polyester or nylon better for swimwear?

It depends on how you plan to use it. Polyester is more durable and chlorine resistant, making it better for regular swimming, while nylon is softer and stretchier, making it more comfortable for occasional wear and fashion focused styles.

Is ECONYL as durable as regular nylon?

Yes. ECONYL is chemically identical to virgin nylon once regenerated, so it performs the same way in terms of chlorine resistance, stretch and durability. Its main advantage is a significantly lower environmental impact rather than any difference in performance.

Why does my swimwear feel fine but look sheer after a season of regular use?

This is a classic sign of chlorine damage to the fibres rather than a fault with the garment. As chlorine breaks down spandex and nylon, the fabric can thin out and lose opacity well before it feels noticeably looser, which is one of the reasons frequent swimmers are usually better off in a polyester or PBT rich blend from the start.

Understanding what your swimwear is actually made of makes it far easier to choose something that suits how you use it, rather than paying for durability you do not need or missing out on it when you do. For the complete picture across every swimwear style, head back to our complete swimwear style guide, or go ahead and shop swimwear built from the fabrics covered here.