EVANS Blue Hydraulic drumheads feature a thin film of oil between two plies of 7mil film offering maximum durability, and a fat, deep and short sound pioneered by early 1970's rock and roll. Single drum head with a thin layer of oil between two plies of film to suppress unwanted overtones Two plies offer consistency and durability for longer playing time A fat, deep and short sound pioneered by early 70's rock and roll Also available in a glass (clear) and a black version Exclusive Level 360 Technology collar design ensures proper contact between drum head and drum shell