Veneer refers to thin slices of wood, usually thinner than 3 mm (1/8 inch), that are typically glued onto core panels (typically, wood, particle board or medium density fiberboard) to produce flat panels such as doors, tops and panels for cabinets, parquet floors and parts of furniture. Veneer is obtained either by "peeling" the trunk of a tree or by slicing large rectangular blocks of wood known as flitches. The appearance of the grain and figure in wood comes from slicing through the growth rings of a tree and depends upon the angle at which the wood is sliced. In addition to the obvious savings of our natural resources, many projects built using wood veneer would not be possible to construct using solid lumber. Due to expansion and contraction common to all wood products and caused by changes in humidity, many of the patterns and designs possible with veneers would self destruct, if attempted with solid lumber. The limitless designs done with marquetry and parquetry would also be impossible.