A felt piano is an acoustic piano that has been modified by placing a strip of felt or other material between the hammers and the metal strings in order to modify its tone color.
The result is a weaker attack and a shorter sustain compared to traditional pianos and thus a reduced brightness and a softer, more mellow and more intimate sound. The felt also reduces the dynamic range by dampening the sound more at higher volumes, making it more suitable for quiet, expressive playing.
The most commonly used type of felt is wool felt. Thicker felt strips produce a more pronounced dampening effect, while thinner strips allow more of the piano's natural sound to come through. Other materials that can be explored for use in "felt pianos" to obtain the desired tonal qualities include velvet, cloth, rubber, leather, plastic and even bamboo.
Although various types of pianos can be converted into felt pianos, it is most practical and most common on upright pianos because they have a built-in mechanism that facilitates the felt's placement, as well as its removal and replacement, thus allowing experimentation with different types of felt and other materials. Some models of grand pianos have also been designed for easy conversion to felt pianos.
Felt pianos are most commonly used in so-called contemporary classical music as well as in ambient music, jazz and other forms of popular music. They are also used extensively in film scores and television, particularly for creating delicate soundscapes for evoking specific emotions.