Bio Plas® brand cryogenic microcentrifuge tubes are sterilized by gamma radiation. These advanced cryogenic tubes have an O-Ring screw cap for a positive, leakproof seal. They are designed for safe storage of cells or biological fluids in the vapor phase of liquid nitrogen or any mechanical freezer. They're ideal for sperm, serum or blood specimens, microbiological cultures, cell cultures and hazardous or valuable samples. These tubes are made from a rugged, precision-molded copolymer and uniform wall construction will stand up to any current microcentrifuge.