There are basically two types of laminate floors as far as the construction is concerned. A direct pressure laminate and a high pressure laminate. The difference appears to be in the process of attaching the materials to the core. The direct pressure laminate is an extended one step process, whereby all the layers are fused directly to the core at the same time, and impregnated with aluminum oxide/melamine resins using heat and pressure. The direct pressure process is used by Formica, and Mannington. On the other hand, the high pressure laminates are a two step wear layer process. First the craft paper type sheets are glued together along with the print film, then this is glued to the core, and everything is bonded together under pressure. Both types of laminate flooring make an extremely hard surface that resist scratching, denting, sunlight fading, and even cigarette burns!
All laminated flooring consists of four main components that are bonded together. A wear resistant decorative surface made of resin based melamine/aluminum oxide. This material is bonded to a moisture resistant wood composition based core. A balancing backing is bonded to the underside of the core. On the top is a clear cap sheet of Aluminum Oxide, which provides the protection and stain resistance.
Most of the cores are made of high density fiberboard saturated in resins to make them extremely hard. This allows the planks to be cut with a tongue and groove for ease of installation. Although the core materials are saturated in resins, planks can still swell from excessive amounts of moisture.
Underneath the core lies another layer, which appears to help stabilize the entire plank and in most cases acts as another barrier from moisture trying to enter from below. Most manufacturers saturate this bottom layer with resins to resist moisture, as well as, make the product more dimensionally stable. This resin filled bottom layer is the main reason these floors cannot be glued directly to the sub floor.