SI-Tack Foam sleeve is a unique add-on device that dramatically improves the sound quality of earphone, in-ear headphones and ear pieces for personal audio products including music players, hands-free mobile phones or handheld computer games. SI-Tack foam sleeve is made by slow recovery foam, is anatomically shaped to fit the ear, making it far more comfortable to use than standard in-ear headphones and ear-pieces, especially over long periods. Made from a Polyurethane slow recovery foam, they are designed to fit the contours of your ears, and so feel really comfortable; and doesn't fall out. 'At last' a solution to stop your old in-ear headphones from dropping out all the time. Why do they sound so better than before? It is made by slow recovery foam. The slow recovery foam have low natural frequency and high sound absorption. The 30db isolated plugs not only isolate the outside noise, the back sound as well. The mixing of front and back sound deteriorates very badly the sound of a headphone or a speaker -- adding distortion and, especially, removing bass.