What are the differences between the materials used?

I have two hats, while I was looking at them I noticed that although they were both 59fifty that they were made out of different materials. One is made of 100 percent polyester while the other is made out of 80 percent acrylic and 20 percent wool. Why do they have different materials and if I was to get another which do you think I should get.

Sorry if this seems like a stupid question I am totally inexperienced and was just curious.