Swim Fabric

Elastane
There is technically one type of elastane, although it is called different names. Spandex is one of them.
Elastane is made up of a long series of polyurethane and is designed so that it can be stretched to a certain limit and returns to its original shape when released. It's similar to rubber, only that it's lighter, stronger, more versatile, and virtually superior in many aspects. Because of its chemical composition, elastane can expand up to 8 times its original size.
Elastane is the preferred material in most swimwear due to its excellent UV-protective quality. On its own, elastane has a UPF (Ultraviolet Protection Factor) rating of 25-39. Study also shows that wet, relaxed, elasticized swim fabric has a good UPF rating, in contrast to non-elasticized knits that are considered inappropriate for UV protection.
Elastane doesn't stand alone but is blended with other types of swim fabric. Wool, rayon, cotton, or even bamboo are common host fibers for elastane. Blending elastane to these materials helps create a fabric that's versatile, resilient, and has excellent shape retention. However, when it comes to swimwear, the usual pairing fabric for elastane is nylon or polyester.
While not at all breathable, elastane has moisture-wicking properties. It's the perfect swim fabric for summer wear because it doesn't show sweat. Moreover, it quickly dries after you've gone out of the water. And since it's stretchy and offers a comfortable fit, it is used by many competitive swimmers. It "sticks" well to the skin and is very light, allowing for better aerodynamics. This is going to be the least of your concern when it comes to children's swimwear, but the fact that your kids are wearing something with no loose openings eliminates safety concerns when they're out swimming.
Because of its strength and elasticity, elastane usually doubles the lifespan of the garment it is blended with. When well taken care of, elastane swimwear can last years. Swimwear made of elastane must be properly rinsed in cool water after each use.

Nylon
Like elastane, nylon is a polymer, which means it is composed of a long series of small organic molecules called monomers. A good analogy for nylon would be a chain, which is constructed using repeated links. Nylon is actually an entire family of materials derived from polyamide monomers extracted from petroleum.
Nylon has excellent strength and is incredibly resistant to abrasion. This is one reason it is used in many sports. It's not as elastic as elastane, but it does have good elastic recovery, which means you can stretch it to its limits, and it won't quickly lose its shape. Nylon also has good resistance to UV rays, which is why it's also a popular choice for many swimwear. While it doesn't offer the same amount of protection against UV rays as elastane, its chemical structure helps boost its sun-protective properties, making it a better option than natural fibers like cotton.
e wearing a nylon shirt, for instance, and you go to the gym or go swimming, water from the pool or sweat will simply rest on its surface and evaporate in a short while.
This water-resistant quality of nylon makes it a superb choice for umbrellas and summer apparel where moisture-wicking is imperative. This particular quality of nylon also protects it from the growth of mold and mildew.
Nylon is also used in sportswear, although it's not considered as superior as synthetic and semi-synthetic fibers like polyester and elastane. While nylon has good moisture-wicking properties, it's not as good as polyester and elastane in this area and is considered a poor choice for most physical activities.

Polyester
Polyester is a synthetic swim fabric derived from petroleum and was introduced into fashion in the seventies. It's not uncommon for some apparel products to be made solely from polyester, although it's more common for this material to be blended with other natural fibers, such as cotton. The result of such a combination is what's known as a poly-blend.
One advantage of blending polyester with cotton is that it helps improve shrinkage and durability. It also reduces wrinkling, and since it's highly resistant to extreme conditions, it is ideal for outdoor applications.
The most well-known form of polyester fiber is ethylene polyester, also known as PET. The process of producing this polyester involves ethylene serving as the polymer that interacts with various chemicals to create a stable fibrous compound. Many of the synthetic products we see and use in daily life are made using PET.
For years, polyester swim fabric has been a leader in the swimwear industry. Whether blended with elastane or by itself, polyester has been a favorite material when it comes to swimwear. Thanks to new technologies, polyester has come a long way in terms of its texture. Compared to other swim fabrics, polyester is more comfortable to the skin, is more resistant to chlorine, and can hold its color for a longer period.
Most people prefer swimwear made from polyester for many different reasons. It's a popular choice because of its high UPF rating, which is usually between 25 and 39 depending on the type of apparel. Polyester itself contains a benzene ring, which absorbs UV light. Shiny polyester clothing is also highly protective against UV rays because it reflects radiation.
Polyester is also stain-resistant. It's especially highly resistant to water-based stains. Since it doesn't easily absorb liquids, it is easier to clean and maintain. Even the most stubborn of stains can be removed simply by soaking polyester fabric in a mixture of warm water and laundry detergent.