Excellent sound quality requires an air-tight seal between the headphone’s diaphragm and the diaphragm in your ear. Overstuffed leather guarantees this air-tight fit. Leather requires over 20 treatment processes before it’s ready to use in manufacturing. One of those processes is dying using polyazo dyes. When used in lower concentrations, these dyes are brightly-coloured; when mixed together and used in very high concentrations, they give an overall ‘black’ appearance to the leather.