Polypropylene co-polymer provides greater chemical resistance than polycarbonate and can be autoclaved repeatedly. Contact-clear tubes allow easy view of contents. Can be used up to 50,000 x g in refrigerated or non-refrigerated centrifuges with sealing cap closure option. Before autoclaving, just set closure on top of the tube without engaging the threads. Must be filled to at least 80% of the total capacity for proper performance. With polypropylene screw closure and silicone gasket.