The term “dampener” is used to indicate that a material is inserted between the strings. For example a strip of paper, felt, foam, rubber, or even folded aluminum foil can be used. The produced sound depends from the type of material: the softer the material, the softer and dampened the sound, the harder and metallic the material, the more percussive the sound.
Different materials can be also placed around single strings, for example a copper wire can be placed around a string and will result in a crackling sound.