Okay, so what's the difference between a multi-layered floor and an engineered floor?
An engineered floor is a 3-layer construction with each layer running at 90 degrees to each other, counteracting the natural movement of wood and creating a very stable floor. The wear layer is normally 3 - 4mm, the softwood core 9mm and the backing layer 2mm, so the thickness of an engineered floor is no more than 15mm. In contrast, a multi-layered floor is usually made up of a wear layer of 3 - 6mm and a number of layers of 1.5mm plywood, all bonded together and running at 90 degrees to each other, creating a very strong floor anywhere between 15 - 22mm in thickness.
So which is better? Generally speaking the thicker the floor, the tougher it becomes, the downside being the increase in cost due to the amount of material used in its construction. Multi-layered floors are however able to support a thicker wear layer which not only makes them a lot more durable but also means that they can be re-sanded and resealed many more times than an engineered floor, giving them a much longer life. Some are thick enough to be used as load-bearing floors and can therefore be laid on joists. Most multi-layered floors have tongue and groove joints which means that they have to be glued together, although in some cases, such as on joists or timber sub-floors, they can be secret-nailed.