Engineered Wooden Flooring is extremely popular, because they are more stable and versatile. The thickness is about 15/14 mm. Top layer is a specie of wood, 3mm and 2mm. Bottom is wooden, spruce or pine or plywood (12mm or 11 mm). It is also very durable.
The base layer provides extra stability as they don't expand or contract as severely as solid wood, when humidity or temperature changes. The real wood top layer, which can vary in thickness, is bonded to the base layer and the movement is then reduced. This makes engineered wooden floor suitable for installation as a floating floor.
