The MTC Bio T8301 5mL Polypropylene Culture Tubes, Dual-Position Plug Cap, 12 x 75mm, 25 per Bag, Sterile, Pack of 1000, are made of high quality polypropylene (PP) plastic that will withstand temperatures from -190˚ to +120˚C. The caps are made of polyethylene (PE) and have the popular two position design (up/loose for aerobic work and down/sealed for anaerobic cultures). The tubes may be centrifuged at up to 4000xg.