Also known as vacuum formers, these machines heat plastic sheets until they're malleable, then use vacuum to form the plastic to a mold. Once the plastic is shaped and cooled, a burst of air separates it from the mold. Thermoformers function best with easy-to-form plastics, such as ABS, polystyrene, and PETG. For best results, create molds using porous aluminum, which allows the vacuum to remove air bubbles. Apply a mold-release lubricant for a clean separation.