This is a wool blend (generally speaking, wool doesn't melt when given the Bic lighter test). It is of decent quality. BUT, it's definitely not genuine US issue and it's definitely not sized for adults. I gave it to my brother-in-law's 4 year old because for this price it's not worth returning.
A genuine US issue cap will have the number RN-93084 printed on the label. This one does not and is therefore fake.

It's a good deal for the price but because of the small sizing and fact that it's not genuine issue as advertised (I doubt the seller knows the difference and was probably fooled too), I have to give it a low rating.