In the world of caps, many materials are used. Some of them are: cotton, wool felt, polyester, and even straw.
Cotton hats are durable, and easy to pack. It can come with a variety of colors and has a softer feel.
Wool felt is created by rolling and pressing wool and applying moisture and heat to interlock them, creating the felt fabric. Wool felt is soft and has a variety of colors as well.
Polyester material is usually combined with cotton. The result is a more durable cap although not as breatheable.
Plastic is also used for Snapbacks. Snapbacks hats uses the term snapback because the cap is adjusted using two plastic pieces that snap together to lock the cap width according to the preferred size.