Experiments were conducted to investigate the effect of plug velocity, plug temperature, and film temperature on the compression resistance of a plug-assist vacuum formed container using high-impact polystyrene. Plug velocities of 0.15, 0.20, and 0.27 m/s; plug temperatures of 25°, 60°, 100°, 123°, and 135°C; and film temperatures of 118°, 125°, 136°, 150°, and 165°C were used in the study. Thermoforming was incomplete when the plug velocity of 0.15 m/s was used in conjunction with the plug temperatures of 25°C and 60°C. Higher compression resistance was obtained when container was formed using the plug velocity, plug temperature, and film temperature of 0.27 m/s, 123°C, and 125°C, respectively. Appropriate stretching time and temperature difference between plug and film are vital for good material distribution and compression resistance of containers during plug-assist vacuum thermoforming. © 1997 John Wiley & Sons, Inc. Adv in Polym Techn 16: 129–134, 1997