Plexiglass, also known as "Plexiglas" or by its chemical name, polymethyl methacrylate, was a strong, transparent polymer plastic used for viewing barriers like windows and aquarium tanks. It was the immediate predecessor to transparent aluminum. Plexiglas is a Genericized trademark commonly used to refer to the material or similar variants. Hikaru Sulu used a Huey 204 to transport the panes of plexiglass across San Francisco to the waiting Klingon Bird-of-Prey, aboard which the tank was to be constructed.