I was in Las Vegas over the weekend and paid a visit to the Star Trek Experience. The hat definitely has a leather-like grain (if it's the actual hat worn by James Cromwell in the film--I have my doubts about the items in the exhibit being screen-used), but the grain is more prevalent than most regular cowhides; horsehide, perhaps? And, unlike most baseball caps which have six seams radiating out from the top, it has only four seams at 90° angles. I'm inclined to agree it was probably made by the costume department at Paramount rather than a modified found object.