1+ skeins Noro Silk Garden Solo (1 for small head, 2 for big)
I love this yarn. Love love love. It's tweedy, mottled, and textured, has a hint of sheen, and it softens and loosens up immensely after a wash! It's idea for the floppiest of slouchy hats. For a larger head consider casting on with a German Long Tail Cast On. We used just over 1 skein of yarn, but could have easily gotten away wit one (my head is small). For a larger size you'll need 2 skeins and to knit the hat a bit longer before crown decreases. For less flop and a tidge more shape try 4.5mm/US7 needles.