Overlaid plywood, which can be either high or medium density (HDO or MDO), is a kind that utilizes the same structure of regular sheets with veneers glued to one another. However, overlaid sheets have an overlaid face that gives it a somewhat finished appearance.
The finished exterior isn’t necessarily for decoration, but instead gives the panels a durable surface that’s also smooth enough to keep water and other particles from damaging or sticking to it. The coating also helps the wood resist scratches and other abrasions that may happen during transport and construction.
Manufacturers bond the exterior surfaces to the rest of the veneers through a process of heat and pressure. High-density overlaid panels have more resin than medium-density panels, making them a bit more expensive. However, both can make a finished project stronger and more durable than can traditional plywood.