The Koss® Plug Classic Noise-Isolating Earbuds are the first of its kind. They deliver accurate acoustical reproduction and unbelievable isolation typically found in more expensive, closed-style headphones. The Plug Classic features a dynamic element that is positioned just outside the ear and connected to a tubular port structure that is inserted on a soft expandable cushion into the ear canal. The soft foam cushion expands for a custom fit to improve isolation and enhance deep bass and treble clarity. The Plug Classic features special ear cushions made of hydrophillic, formed urethane, for a custom fit each and every time it is inserted into the listener’s ear. The custom fit enhances isolation when you want to plug out ambient sounds that interfere with the listening experience. The Plug Classic has a frequency response performance of 10 Hz to 20 kHz and the full Sound of Koss. Combined with your favorite music and a portable sound system, it is the ultimate accessory on the go. 4 extra ear cushions are included.