Product Information: EVANS Marching EC2S series features two matching plies of 7mil film for greater strength and durability. Sound Shaping Technology (SST) controls overtones for focused sound. The hoop profile is specially designed to withstand higher tensions and offer greater durability. Product Features: Two matching plies of 7mil Sound Shaping Technology (SST) controls overtones for focused sound For more information and specifications, please refer to the manufacturers website