Made of medical grade polypropylene; Can be repeatedly frozen and thawed Self-Standing and external threads Vials have a white writing area and black graduations ?1D barcode and human readable numbers on side CryoKING Combo: 2D Barcoded Cryogenic Vials and compatible polycarbonate Cryogenic Boxes are available as a set Gamma radiation sterilized; DNase & RNase free, endotoxin free, foreign DNA free Working temperature: stable from -196℃ to 121℃? Suitable for liquid nitrogen freezing