These disposable microtubes are designed for use in all popular microcentrifuges. They are manufactured from precision molded polypropylene for biotechnology applications. The cap design allows repeated openings and closings yet resists popping from internal pressure or during boiling. Natural Polypropylene Non-Sterile Grad Lines: Yes Certified RNase/DNase Free Certified Human DNA Free Certified PCR Inhibitor Free Certified Pyrogen Free 400 Tubes/Bag, 10 Bags/Case