The waves or corrugations of the medium are called its flutes. Letters are used to designate flute size, with C-flute board being by far the most common material for corrugated shipping boxes. B-flute is a smaller flute size that is sometimes used when high compression strength is not required (for transporting canned goods, for example), while A-flute is a larger size that can be used for cushioning, especially in the form of single-face board. In double-wall and triple-wall corrugated board, corrugating mediums of different flute sizes are often combined in order to take advantage of their different benefits.