Exterior caps with silicone gaskets seal in the vapor phase of liquid nitrogen. Long-skirted caps minimize contamination during handling and require only 1 turns to close. Each tube has easy to read graduations and a large, white labeling area. Tamper-evident, re-closable bags are gamma sterilized. Polypropylene. RNase, DNase, DNA free and non-pyrogenic. Measures 12.5 x 48 mm.