SureSeal™ sterile screw-cap microtubes come in a variety of sizes, cap configurations, graduation options, and now light-blocking amber. 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 SureSeal™ screw cap microtubes are sterile, RNase, DNase, & pyrogen free and may be centrifuged at up to 22,000xg.