Globe Scientific's 12mm plastic culture tubes are produced in polystyrene or polypropylene. The polystyrene tubes can withstand 1500 RPM during centrifugation. polypropylene tubes can withstand 3000 RPM and are autoclavable and freezable. Plastic culture tubes with polyethylene dual position snap caps provide either aerobic or anaerobic storage of samples. Note - Leave the dual position snap cap in the loose position for aerobic work and in the sealed position for anaerobic cultures.