Ancient Egyptians created what may be the earliest version of what we know today as plywood! Realizing that wood was stronger across its grain than parallel to it and that thinner pieces, while more flexible, could barely support any weight, workers glued thin slabs of wood together with their grain running perpendicular to each other. The strength of one ply compensated for the weakness in the next. The glue used to bind layers together in today’s plywood is phenol-based.

A DVD is composed of several layers of plastic, totaling about 1.2 millimeters thick. Each layer is created by injection molding polycarbonate plastic. This process forms a disc that has microscopic bumps arranged as a single, continuous and extremely long spiral track of data. Once the clear pieces of polycarbonate are formed, a thin reflective layer is sputtered onto the disc, covering the bumps. Aluminum is used behind the inner layers, but a semi-reflective gold layer is used for the outer layers, allowing the laser to focus through the outer and onto the inner layers. After all of the layers are made, each one is coated with lacquer, squeezed together and cured under infrared light.

Each writable layer of a DVD has a spiral track of data. On single-layer DVDs, the track always circles from the inside of the disc to the outside. That the spiral track starts at the center means that a single-layer DVD can be smaller than 12 centimeters if desired.