Why are there dents on the top of cowboy hats?

Most cowboy hats were sold “open crown”, meaning no shaping. It was a cowboy’s preference to dent and pinch his crown for his own style or need. Hats were dutiful, comfortable, and stiff brimmed. Some men wore Mexican sombreros in woven straw or felt. Some liked the short brimmed bowlers with high-mounded crowns. In all, the pinch was a Gus crease down the middle front, the Montana Peak with four equal dents on a high 6-inch crown, a telescope-styled based on making a circular crease so the top of the head fit tightly into the crown, and a hand worn pinch with a forward crease and two side dents. Mostly that style was just something that happened with wear, and not necessarily a style at all. Most hats were filthy, well worn and damaged from being used so much. Individual style was shown in the hatband: ribbon, high or narrow, a horsehair braid, a leather twist with knots or braid, or a simple narrow leather band. I prefer a braid with a matching chinstrap.

http://www.curtrich.com/hats2.html

Today, the dents in cowboy hats are there for style only.

http://www.stetsonhat.com/