"ClearSeal sterile screw-cap microtubes come in a variety of sizes, cap configurations, graduation options, and even a loop-cap option for the 2.0mL. Made from ultra-clear polypropylene, these screw-cap microtubes include assembled caps with silicone O-rings that assure a leakproof seal from -90°C to +121°C. All ClearSeal screw cap microtubes are sterile, RNase, DNase, & pyrogen free and may be centrifuged at up to 22,000xg*. Ultra-clear polypropylene Packaged in resealable bags of 50 Leak-proof O-ring seal Sterile, RNase, DNase & Pyrogen free White, printed graduations"