There are a number of different swimming caps and each of them are made from different materials and are for different purposes. The most popular ones are latex and silicone.
Silicone
Silicone caps are thick, long-lasting, and durable. The material that they are made from makes it easy to put on and take off. These types of Latex swim caps fit nice and tightly on your head, which keeps a lot of the water away from your head.
The one downside of silicone caps is that they often tend to slip off, which can be a huge pain in the behind. This can be a serious problem when you are racing. Silicone caps are soft and stretchable, which makes them very comfortable to wear.
Latex
Latex swim caps cost much less than silicone ones do, and they are very thin, which makes for a much better grip on the head. The thin material that latex caps are made from makes them less durable. They tend to be less comfortable than silicone caps, and certain people are allergic to latex, which makes them unsuitable for them.
Lycra
Lycra caps are the most comfortable of all swimming caps and this is due to the fact that they are made from the same material as wet suits. These types of caps are not recommended for racing, as they often slip off while swimming. Lycra swimming caps do not offer the user any protection from the chlorine in the water, nor do they reduce any drag. These types of caps are recommended for water aerobics or any other water-based activities where you are not fully submerged.
Neoprene
These types of caps are also made from the material that wet suits are made from. These swimming caps are used for swimming in the open water and give that bit of extra warmth to the users. They have a chin strap that is designed to keep the ears warm while swimming. Neoprene caps are generally only used for open water swimming competitions that occur in colder climates.
One downside of these types of caps is the fact that they are pretty thick, which could feel a bit tight on the head. They also happen to be the most expensive type of swimming cap on the market at the moment.
So, the type of swimming that you will be doing will decide what type of swimming cap it is that you will need.