Hardwood planks classified as “engineered” feature multiple layers (typically three to five) bonded together under extreme heat and pressure. The layers typically include a top veneer of hardwood backed by less expensive layers of plywood—although some manufacturers use substrates made from recycled wood fibers mixed with stone dust for improved durability and stability. Because of the way engineered hardwood is processed, it is not as affected by humidity as solid wood planks are. Therefore, the product is often the preferred choice for kitchens and bathrooms or in areas where the humidity level can vary—like in a basement or a part of the house below grade, as long as a moisture barrier is placed between the subfloor and the hardwood planks. They are also better suited for installing over in-floor heating systems. Engineered hardwood floors are suitable for installation on all levels of the home and over plywood, wood, OSB and concrete subfloors.