These disposable, sterile, round-bottom 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 more limited temperature range of 0˚ to 70˚C. Caps are made from 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 can withstand higher forces, up to 4000xg.