In architecture and design, paneling, often written panelling, is a decorative treatment of walls, ceilings, doors, and furniture made up of a sequence of large, thin sheets of wood called panels that are bound together by thinner, thicker strips of wood. The word "panel" comes from the French pannel, which in turn comes from Latin pannus, meaning "a piece of cloth," or "a skin." In construction, a panel is a thin sheet of wood or other material used to cover a surface. Panels are used to create walls, floors, and other structural elements of buildings. All wood is composed of cellulose fibers wrapped around groups of water molecules. Wood is classified as hard or soft based on how much fiber there is per unit weight. Hardwoods have more fiber density so they're heavier than softwoods. But because hardwoods are more dense, they tend to be more brittle. Softwoods are less dense so they're more flexible and can be used for lighter work. However, they aren't as durable so they tend to need maintenance treatments such as oiling or waxing to keep them looking good over time. Paneling is usually made out of wood because it's strong and sturdy, but other materials could be used instead. For example, particle board is made out of polymers and wood flour mixed with heat and pressure to make one solid piece of material.