These disposable sterile tubes are made of high quality polypropylene (PP) plastic that will withstand temperatures from -190˚ to +120˚C. They are also available in crystal clear polystyrene (PS) with a ange of 0˚ to 70˚C. Caps are made of polyethylene (PE) and have the popular two position design (up/loose for aerobic work and down/sealed for anaerobic cultures). Polystyrene tubes may be centrifuged at up to 2000xg. Polypropylene tubes withstand higher forces, up to 4000xg.