It uses alpaca. The droopy slouchy factor is built in!
It has enough looseness to look haphazard,but not enough so as to look like you borrowed it from someone bigger headed.
Single crochet around the brim ensures a firm tight crown at the business end so that the textured fabric can do what it likes without falling off your head. Sometimes, in an attempt at volume, these hats contract too quickly creating a mushroom cloud hat or they overcompensate by ending in a very tight edge. Here, the brim is worked first.
It's crocheted, it's textured, and yet it takes 1 skein! (just)
As to inspiration;