Polypropylene tubes include blue HDPE leak-proof screw caps. The tubes and caps feature specially-designed flat threads for vacuum-type closure that is leak-free at a pressure of >700mm Hg. Highly smooth hydrophobic internal surfaces minimize wall effect. Silk-screen graduations and a frosted surface make writing easier. Autoclavable at 121°C and 15 psi for 20 minutes. Gamma radiation sterilized. DNase, RNase, Pyrogen and latex-free. Maximum RCF 18,000 (15 mL) and 20,000 (50 ml). Amber colored tubes are suitable for light sensitive applications because they do not allow any light to pass through the samples.