The material decide by the customers choose, and the caps function and shape.
Different customer has the different prefer of the caps material , some brand like suede , and wool bent material (It seems high quality), fake wool (feel as wool , new era even use it for the cheap caps)
The common material is cotton which always use for all kinds of caps .
Mesh is always use for customized sports caps , it is breathable and good sweaty.
We can check the material pic by custom ball hats page .