The Koss Plug revolutionized the world of in-ear headphones. A first of its kind, these are stereo, noise isolating in-ear headphones that deliver the kind of accurate acoustical reproduction and isolation typically found in high-end, closed-style high fidelity headphones. A dynamic element positioned just outside the ear connects to a tubular port structure that inserts into a soft, expandable cushion. The soft, foam cushion expands for a custom comfort fit with every listening experience. It also improves isolation, plugging out ambient sounds, and enhances deep bass and treble clarity.