A cutting board (or chopping board) is a durable board on which to place material for cutting. The kitchen cutting board is commonly used in preparing food; other types exist for cutting raw materials such as leather or plastic. Kitchen cutting boards are often made of wood or plastic and come in various widths and sizes. There are also cutting boards made of glass, steel, or marble, which are easier to clean than wooden or plastic ones such as nylon or corian, but tend to damage knives due to their hardness. Rough cutting edges—such as serrated knives—abrade and damage a cutting surface more rapidly than do smooth cutting implements. A knife edge is a delicate structure and can easily be blunted by a too abrasive surface. Alternatively, it can be chipped if used on a surface that is too hard. A good cutting board material must be soft, easy to clean, and non-abrasive, but not fragile to the point of being destroyed. Hard cutting boards can, however, be used for food preparation tasks that do not require a sharp knife, like cutting cheese or making sandwiches