I think it was wool? Could that even be possible....maybe corduroy. It was much fuzzier than caps today.
Funny thing is I wore that cap all the time for 30 years. Eventually it became my painting hat and finally, while it was sitting on my workbench in the garage, a bird got stuck in my garage and was flying all over the place trying to get out (even though the big garage door was wide open). While it was flying, it was so scared it started pooping all over the place and guess where some of this poop landed? Right on my hat! Needless to say, the hat went into the garbage but I got a lot of good use out of it as well as some great memories.