A method of forming thermoplastic polymer matrix composites into three dimensional shapes, in which the plastic sheet is clamped in a frame suspended above a mold, heated until it becomes softened, drawn down into contact with the mold by means of vacuum, and cooled while in contact with the mold. Matrix resins used for composites include ABS and ABS alloys, PVC, PPO, acrylic, polystyrene, polyethylene and polycarbonate.