Swim Caps
You can find swim caps online with TriShack. There are lots of options when it comes to swim caps and usually depends on personal preference - some of the different types include Latex, Silicone, Lycra and Polyester.
To makesure you choose the right fitted swimming cap, take a measurement with a soft tape measure around your head where your swim cap would normally sit. You can then use this measurement to help you find the right size cap. A cap that is too small will start to dig into your forehead and scalp which will in turn give you a headache. A cap that is too loose will increase your drag in the water along with possibly just pulling free with some water resistance.