Swim caps are not expensive, but even so choosing one can be difficult because there are a number of different materials, styles, and colours. In many countries you are required to wear them, but this is not the case in the UK. Some pools do insist upon them, but by no means all.
Many people think that you wear a swim cap in order to keep your hair dry, but a swim cap doesn't create a waterproof seal round your head, and some water will always get in. The only practical way to keep your hair dry is to swim with your head out of the water, as in breast stroke.
Nevertheless, there are some good reasons to wear a swim cap, one of which is that if you have long hair it will keep it out of your face. If you are swimming in a pool it will keep the chlorine in the water from damaging your hair. There is evidence that chlorine can cause the hair to become dry and brittle, and the scalp to become flaky, which could lead to some hair loss.
Some people are surprised to learn that you can prevent chlorine damage by wetting the hair thoroughly before swimming. Hair has the ability to absorb water in the same way as a sponge, and by wetting it first you help to prevent it from soaking up chlorinated water. You also need to wash your hair thoroughly with shampoo after swimming in order to remove all traces of chlorine. If your hair is dyed there are special shampoos and hair conditioners that you can buy that will minimise discolouration. A swim cap will also help to keep as much of the chlorinated water out of your hair as possible.
Some pools do insist on wearing a swim cap because it also helps to keep hair out of the pool water filter.
Another advantage of wearing a swim cap is that a brightly coloured one can make you more visible when you are swimming in open water, so there is far less risk of being hit by a speedboat towing a skier, or any other boat for that matter. In addition, wearing a swim cap can help to keep your head warmer when swimming in open or cold water, especially if it is made of neoprene. It also helps to reduce drag, so if you are swimming in a competition it will help you to swim just a little bit faster.
By far the most popular swim caps are those made of silicone. They are a little more expensive than latex rubber swim caps and were developed because some people are allergic to latex. They are easy to put on and take off, but they have a tendency to slip more than latex. They come in a huge range of colours and patterns. Latex swim caps, by contrast, are a tighter fit than silicone, and are the type preferred by competitive swimmers because the tight fit makes for a more streamlined configuration in the water, and thus helps with speed. It is also easy to print on latex and for this reason they are often used in triathlons where numbered swimming caps may be required.
Lycra is another material that is used for swim caps and they are more comfortable than latex or silicone caps. They are also longer lasting. However, they do have a disadvantage, and that is they slip a lot which means that they let in water so won't keep the chlorine out of your hair. This also means that they don't have the same effect of reducing drag.
Neoprene is the same material that wetsuits are made of and these numbered swimming caps are great for use in triathlons because they are thicker than other caps and they keep your head warmer in cold water. You can actually lose quite a lot of heat through your head when swimming in cold water, so neoprene caps are the answer.
As for styles, there are bubble swim caps which have more of a helmet shape and are covered all over with bubbles. There are also bigger swim caps for long hair, and there are some fun ones that are covered in pretty flower effects or for the kids, swim caps with eyes and a fin at the back made to look like a shark.