High-density Ultra-Suede which is an excellent silencer material. The Grey Ultra-Suede is more useful on smaller keys such as the top stack of alto saxophone, flute and clarinet and will not compress a readily as felt or the thicker ultra-suede. Excellent for noise reduction where a thin cork might otherwise be used. The Black Ultra-Suede will be more useful on larger keys where noise reduction is essential such as the lower stack keys in a Tenor Saxophone. The White Ultra-Suede offers more flexibility.