While I admit finding a valve guard for a cornet will be extremely difficult, the instruction Rick gives to make one's own is inadequate and itself cause more problems than gains. Tanned leather leaches tannic acid as will in time "eat" at the valve finish. These guards are made of three layers, tanned leather, waterproof plastic film (Mylar(R)) and soft cloth inner layer. As others say, they are still collectors of grit. Too, they must be removed for proper cleaning of the instrument. This said, I would not even suggest that a beginner use one, and I would not allow a beginning student to use one were I tutoring them. They instill a habit that will be later disallowed in band competition, show, and concert.